I have 2 primary needs, Media playback and NAS. My current board is the Odroid XU4Q is unfortunately not living up to my expectations but it's been a good learning process. It has problems with thermal throttling and does not have hardware decoding for H264/H265 so I get tearing and low framerates even at 1080P. Youtube is 720P. I also had issues with UAS protocols and had to disable it on my USB3.0 attached HDD. (This has more to do with my USB to SATA cable than anything else). After a fair bit of research I've decided on the RK3399 SoC.
Too big for my liking. Due to thermal issues most people run it at 1.8Ghz big and 1.4Ghz small. I also really don't like that you need a PCIe expansion board for SATA. There have been a lot of issues on the forums for this board, especially with the SATA expansion board.
I can't find much info about using the M.2 M-Key with a SATA expansion board. Only report I found of someone trying this said due to the positioning of some components their board shorted. No board released directly by FriendlyElec for this purpose so drivers will also be an issue. RK3399 SoC on the top of board so likely thermal issues.
Checks off all the boxes nicely. Great heatsinks, 4xUSB3.0 and there's a HAT in development with 4 SATA ports and 2 Molex ports. I love the form factor, it has great reviews, the price is reasonable. With a small fan you can even overclock it slightly.
Could maybe work for me if they make a SATA HAT like they have for the M4, otherwise existing connectivity ports are inadequate. Also 1GB Ram is a little lean. I would still love one of these down the road to tinker on.
Cancelled, otherwise this would have been a strong contender. It has on board SATA support and a large community to back it up. Still waiting to see what Odroids going to come up with next.
Other Manufacturers of RK3399 boards.
The older RK3399 boards all seem to be more expensive, lacking in SATA options and cap at 2GB RAM. None of them really caught my attention.
X86 boards like UDOO and LattePanda
Too expensive for what they were offering. Less power efficient.