Security wise i would say newer is better. For me personally the hardware video decoding is not relevant.
Do you have any ideas for my battery drain problem? I know a lot of people have to charge their phones on a daily basis, but if you’re used to have 3-4 days it’s really annoying.
I am not using your build (yet), but I would say release it with Android 6 first. From Ubuntu Touch, I know that hardware decoding bugs can be long to solve, see the Nexus 5 which still doesn’t have hardware acceleration for example. So solving this could delay the release for some time, and I see no reason to do so.
I guess you also want to release an “alpha” image based on Android 7 to some power user before pushing that to OTA, no?