olivluca

I do remember some discussions on OpenELEC forum (it is completely ruined now, unfortunately)  about NEON optimizations, which improve h.265 playing. 

I can be wrong but seems like Amlogic should support hw decoding.  I my personal experience with LibreELEC/CoreELEC on Le Potato is kinda "mixed".  I wouldn't recommend it as a replacement for RPI3 at least right now. 

Yes, indeed RPi3 is a good choice. The only drawback is that h.265 being software decoded because the VPU/GPU part has not been updated since their debut, on the other side you get plenty of support by community and foundation, and also an opensource GPU OpenGL driver which works pretty well, as opposite of the crappy blobs for ARM Mali GPUs

Hi,
TLDR: RPI3 is a very good option. 
I've got RPI 3B now. It runs LibreElec smoothly. Previously, I had RPI 2 and even RPI 1 (which is like zero almost). In general, RPI3 works great, I've got no serious complaints just a nit-picking.  
 
IMHO there are few important points (your mileage may vary): 
*) 1GB and 2 cores make a huge difference 
*) A lightweight OS like LibreElec, OpenElec whatever.  Do not waste resources. I tried Raspbian, Xbian and OSMC. They are all good but LibreELEC flavors are just better. 
*) My RPI3 has a root filesystem on a USB thumb drive, it is faster and more reliable. 
*) A good PSU as always. 
 
Now I'm experimenting with AML-S905X-CC (Le Potato) and LibreELEC. It is a very nice board but frankly, it is not a real competitor so far. 

Well, you should at least specify the hardware you want to run armbian and kodi on.
If your intent is to just run armbian + kodi, usually you get most hardware acceleration (GPU + video decoding) if you use the kernel provided by the hardware manufacturer, but don't expect a warm soup ready for lunch.
Each SoC is a different story: GPU drivers are not always available (mostly due to ARM Mali license, the most common GPU in SoCs), and sometimes they are misbehaving. It's kind of puzzle-game where not always all the pieces are there to be fit togheter.
 
At the moment, I don't know any board which works out-of-the box with vanilla armbian.
Some work has been done by the community for rockchip rk3288 (see here). Rockchip are the most promising because the manufacturer provides documentation and source code and also GPU drivers works.
Allwinner provides GPU drivers for their old Mali400/450 GPUs. Bootlin reverse engineered the VPU on older SoCs (H3 and going back) to provide hardware acceleration for videos on mainline kernel and apparently some support is appearing in ffmpeg, although I don't know if it is ready to be used.
AmLogic is unknown to me, I think you should stick to their white-beard old kernel if you want GPU and VPU acceleration
 

I don't know if the CSI connector on the pi zero plus 2 is the same as the pi pc, it seems so but one never knows.
OTOH the gc2035 driver in armbian has several issues (search the forum for gc2035). I'm using an older version of the driver (which has a different set of issues but it works better here).