If you want really open then OpenWRT and a Banana Pi is the way to go. OpenWRT is compatible and well supported on this board wiki.banana-pi.org/Banana_Pi_BPI-R3. There’s a new coming up, the wiki.banana-pi.org/Banana_Pi_BPI-R4. Banana Pi invest a lot in supporting OpenWRT and they don’t provide any other option and the chips are MediaTek that kind of views Banana Pi as a testing ground for their next gen stuff.