The A20 is quite good supported as long as you stay with the old Kernel 3.4 - unless you are a programmer, a GPU driver is not ready until the development ist finished, right?
You are very smart to get information before purchase - most do different.
If you want a Banana, there are only 3 models to recommend, well basically 2.
* Banana Pi BPI-M1
* Banana Pi BPI-M1+
* Banana Pi BPI-M2U (careful, brandnew no SW available)
Basically you have to get the software from the armbian geeks www.armbian.com.
The Banana's have not much time or know-how about SW, beside that they hardly fix a bug even if you put it on github.