Even though I prefer the ATV interface more, I have switched to the Nvidia shield. The app experience, in particular Netflix, is way superior. I've noticed Plex is a bit more feature rich on AndroidTV.
My experience is just the opposite. Shield is great when it works, but:
1. loses audio. Reboot.
2. Plex sometimes plays certain titles at multiple X speed. Reboot.
3. Plex just hangs with spinning circle. Reboot.
Have never experienced (2) or (3) on Apple TV.
and many more problems that I can't remember right now ...