I'm sure 720p baseline should be fine with any player. 1080p baseline should be fine. Probably main profile too. The problems arise with high profile HD material, which unfortunately is what a lot of stuff out there is encoded with. Then again, I guess most people aren't going to stuff HD movies on their tablets. The 4GB max file size on fat32 gets in the way as much as anything else .
As an aside. I've been using Plex server to transcode and stream movies (including bluray rips) from nas to tablet (running Plex player) with excellent results. But that's probably best left for another topic...