TL;DR: All available H3 boards do not differ that much. But the few differences sometimes really matter!
The following is an attempt to compare the different available H3 SBC that are supported by Armbian. The majority of boards is made by Xunlong but in the meantime two more vendors started cloning the Xunlong boards (and also Olimex is preparing H3 boards as OSHW). Both Foxconn/SinoVoip with their Banana Pi M2+ and FriendlyARM with their NanoPi M1 tried really hard to copy everything as exact as possible (the so called pin mappings -- how the many contacts the used H3 SoC is providing are routed to the outside).
All the boards share the same 40 pin GPIO header (trying to be compatible to the newer RPi boards) and since all the other pin mappings are also 99 percent identical you can for example boot a NanoPi M1 with an Armbian image for Orange Pi PC without loosing any functionality (except of camera module) and the same applies to BPi M2+ that will boot happily an Armbian image for Orange Pi Plus 2E (except of camera module and WiFi/BT)
In fact all the various H3 boards just differ in a few details:
Amount of DRAM
No, Fast or GBit Ethernet
Voltage regulator and 'thermal design' (responsible for performance in full load situations)
Storage capabilities (pseudo SATA and eMMC or not)
Count of available USB ports (with or w/o internal USB hub)
Some additional features like camera modules, WiFi/BT and additional/optional connectors (here it's important to check for driver functionality/availability. If there's no driver providing the necessary functionality then these 'additional features' are pretty much useless -- camera connector for example)
Why focussing on the H3 SoC for this comparison?
Since some of these boards are priced pretty competitive
Mainlining support for H3 SoC and these boards is progressing really nicely so we'll be able to run these boards with mainline kernel pretty soon (thanks to the great linux-sunxi community)
2D/3D/video HW acceleration is available with legacy kernels (again thanks to the great linux-sunxi community)
The feature set is nice for many use cases (quad core SoC, GBit Ethernet and 4 useable USB ports on some boards make a really nice low cost/power server)
It got somewhat confusing regarding the many available Oranges and now also the cloned Banana and NanoPi
This is also in preparation of a broader overview of the capabilities of all the boards Armbian currently supports now focussing on the H3 family. So let's get into details:
Amount of DRAM
That's an easy one. The H3 SoC supports up to 2 GB DRAM. The available and announced boards use either 512MB, 1 GB or 2 GB DRAM (low-power DDR3L on the bigger Oranges and DDR3 on OPi One/Lite, BPi M2+ and NanoPi M1). In case you're using Armbian it simply depends on the use case. And also it's necessary to understand that Linux tries to use all your RAM for a reason: Since unused RAM is bad RAM. So don't be surprised that Armbian will eat up all your RAM to cache stuff which improves performance of some tasks but the kernel will immediately release it when other tasks have a demand for it. If still in doubt please enjoy http://www.linuxatemyram.com.
If you want to use your boards with the unofficial H3 OpenELEC fork too please be aware that OpenELEC benefits from at least 1 GB RAM since then the whole filesystem remains in memory and no accesses to a probably slow SD card happen. Prior to jernej/OpenELEC and Armbian resolving the kswapd bug a few weeks ago the 512 MB equipped boards performed rather poor. But now it seems that the unofficial OpenELEC fork runs pretty well also on the boards with less available RAM.
Whether 1 vs. 2 GB RAM make a difference absolutely depends on the use case and no general recommendations can be made.
Since OpenELEC has been mentioned it should be noted that the current implementation of the unofficial OpenELEC port for H3 boards makes use of the cedarx-license-issues-library (no clear license preventing the use if you care about legal issues -- please have a look at http://linux-sunxi.org/Kodi for further details)
The H3 SoC contains an Ethernet implementation that is capable of 10/100 MBits/sec Ethernet and also GBit Ethernet. A PHY (that handles the physical interconnection stuff) for Fast Ethernet is already integrated into the H3 SoC but to be able to use GBit Ethernet an external GbE capable PHY is needed (the RTL8211E used on all boards adds approx 1.2$ to the costs of the board in question).
Most H3 boards use the internal Fast Ethernet PHY so wired networking maxes out at ~95 Mbits/sec. Orange Pi Plus, Plus 2, Plus 2E and BPi M2+ provide GBit Ethernet (+600 Mbits/sec with legacy and exactly 462 Mbits/sec with mainline kernel) while Orange Pi Lite saves an Ethernet jack at all. The good news: Even with the Lite you can use wired network adding a cheap RealTek USB3-Ethernet dongle like this which is confirmed to exceed 300 Mbits/sec in a single direction.
The currently available boards have either no WiFi (NanoPi M1, OPi 2 Mini, One and PC), rely on RealTek 8189ETV (OPi 2, Plus, Plus 2), the newer RealTek 8189FTV (OPi Plus 2E, Lite, PC Plus) or a WiFi/BT combination: AP6181 is used on the BPi M2+ but the vendor didn't manage to get BT working at the time of this writing. Currently only jernej's OpenELEC fork and Armbian have a working driver included for the new 8189FTV chip on the fresh Orange boards that seems to perform quite ok and provides client/AP/monitor mode. Can't say that much about that since in my very personal opinion all these 2.4GHz onboard WiFi solutions are simply crap
Voltage regulator and 'thermal design':
This is a very important differentation: All Orange Pi boards use a programmable voltage regulator to adjust the voltage the SoC is fed with. The SY8106A used on every Orange except of One and Lite can be controlled though I2C and adjusts the so called VDD_CPUX voltage in 20mV steps. This is important since 'dynamic voltage frequency scaling' relies on the principle of providing less voltage to the SoC/CPU when it clocks lower. So when the board is idle also the supplied voltage will be reduced resulting in less consumption and also less temperature.
Since H3 is somewhat prone to overheating being able to adjust VDD_CPUX is also important when we're talking about the opposite of being idle. The SY8106A equipped Oranges reduce very fine grained the core voltage when they start to throttle down in case overheating occurs under constant heavy load. As a direct result they will automagically perform better since reducing VDD_CPUX voltage also reduces temperature/consumption so both CPU and GPU cores in H3 due not have to throttle down that much.
Quite the opposite with BPi M2+. For whatever reasons SinoVoip saved put a the same programmable voltage regulator on their board as OPi One, Lite and NanoPi have but does not implement voltage switching so H3 there will always be fed with 1.3V. In addition it seems 'Team BPi' didn't take care of heat dissipation through PCB design (it seems Xunlong added a copper layer to the PCB that helps dramatically spreading the SoC's heat) and so with BPi M2+ (and NanoPi M1 too) you have to be prepared that you need both a heatsink and a fan to let this board perform under full load since otherwise heavy throttling occurs or when you use a kernel that does not implement throttling (4.6/4.7 right now for example) be prepared that H3 gets either destroyed or will crash through overheating if you run something heavy on BPi M2+ or NanoPi M1. We're still investigating whether this crappy thermal behaviour might be related to DRAM also (DDR3 vs. low power DDR3L on the Oranges) It seems this thermal behaviour is not that much related to the DRAM type used but more to PCB design (maybe using large internal ground/vcc planes optimizing heat dissipation on Oranges.
NanoPi M1 and Orange Pi One/Lite use a rather primitive GPIO driven voltage regulator that is able to just switch between 1.1V and 1.3V VDD_CPUX which already helps somewhat with throttling.
A rather demanding benchmark using cpuminer (a bitcoin miner making heavy use of NEON optimizations and assembler instructions) that knows a benchmark mode where it outputs the khash/s rate. On the left OPI+ 2E with the superiour SY8106A voltage regulator switching CPU frequency between 1200 and 1296 MHz. On the right little OPi Lite with the SY8113B voltage generator able to switch between 1.1V and 1.3V and with slightly lower performance since throttling prevents clocking that high. And in the middle as only board with applied heatsink on H3 poor Banana Pi M2+ using the same SY8113B voltage regulator but always feeding the H3 SoC with 1.3V (for whatever reasons!).
The H3 SoC doesn't feature native SATA capabilities so the 2 boards that have a SATA connector (Orange Pi Plus and Plus 2) implement that using an onboard USB-to-SATA bridge. Unfortunately the chip used there -- a Genesys Logic GL830 -- is horribly slow limiting sequential transfer speeds to 15 MB/s write and 30 MB/s read. It also does not support the USB Attached SCSI Protocol (UASP) so when using mainline kernel attached disks an especially SSDs couldn't show their full random I/O performance.
Given that common USB-to-SATA bridges used in external USB enclosures show way better sequential performance (35 MB/s in both directions and close to 40 MB/s when using an UASP capable bridge together with mainline kernel) the SATA port on these 2 SBC can not be considered a feature worth a buy.
Every H3 board has a TF card slot (Micro SD card) and some of the boards feature onboard eMMC storage. The H3 can cope with TF cards that are compliant to the SD, SDHC and SDXC standards so rather large cards with more than 64 GB capacity can also be used (be aware that there do not exist that much cards with a capacity larger than 128 GB. Chances are pretty high to get a counterfeit card especially when the price looks too good to be true ). You should also be aware that all H3 boards show the same sequential speed limitations (maxing out at ~23 MB/s) so choosing cards that are rated way faster aren't worth a buy. Better have a look at random I/O performance that is more important in most use cases.
The eMMC used on various boards is pretty fast (sequential speeds maxing out at ~75 MB/s and especially random IO way faster than the fastest tested SD cards which is important for desktop useage and databases for example) so you don't make a mistake choosing any of the eMMC equipped H3 boards (BPi M2+, Orange Pi Plus, Plus 2, Plus 2E or PC Plus). You find detailed test results of current SD/TF cards as well as all the eMMC variants used in these two threads:
Count of available USB ports:
The H3 SoC features 3 USB2.0 host ports and one USB OTG port. With Armbian we configure the OTG port as a host port that shows pretty similar performance so on some H3 boards (Orange Pi PC, PC Plus and Plus 2E) you can benefit from 4 USB2 ports that do not have to share bandwidth.
Some other boards use an internal USB hub (Orange Pi 2, Plus, Plus 2) so the available USB ports have to share bandwidth in reality. Please keep that in mind when you compare the 4 USB Type A jacks OPi 2, Plus or Plus 2 feature (all being connected to a USB hub so having to share the bandwidth of a single USB 2.0 host port) with the 3 you can count on OPi PC, Plus 2E or NanoPi M1. On the latter boards you get full USB 2.0 bandwidth on each USB receptacle without the need to share bandwidth.
BPi M2+ does also not use an internal USB hub but only exposes 2 USB host ports on type A receptacles and the 3rd host port only without ESC protection via soldering (but since this board shows such a terrible thermal design and is relatively overpriced compared to other H3 boards that doesn't matter that much)
The only board featuring a Bluetooth capable chip from BroadCom is the BPi M2+. Currently the vendor admits that BT is not working so better don't count on this feature to be ever available.
Update: Jernej got BT already working in his OpenELEC fork so it's just a matter of time until it works with Armbian too.
The H3 SoC is able to output/intercept additional signals, eg. analog audio, Composite video (TV out), IrDA that are present on most of the boards. On the Orange Pi One many of those interfaces are only present as solder points (a bit too tiny to be used by the average maker) and on some other boards they are not present at all (BPi M2+ for example has neither composite video nor analog audio) so always check first what you need or want to use.
We have a nice sortable table in linux-sunxi wiki showing most of the important details: http://linux-sunxi.org/Table_of_Allwinner_based_boards
Xunlong provides a pretty cheap 2MP camera module that should work with every H3 Orange Pi out there (they all have the necessary connector but for OPi One, Lite, PC and PC Plus you have to tell Xunlong that you also need a so called 'expansion board' that they ship free of charge if you add to your order that you need it. Starting with Armbian release 5.15 we also include an improved driver for this camera.
Regarding current state of available camera modules for Oranges, BPi M2+ and NanoPi M1 please look through this thread: http://forum.armbian.com/index.php/topic/1213-ov5640-camera-with-orange-pi/?view=getlastpost