The Mi Boxes all have relatively similar, not particularly powerful hardware. With 4K playback, this can lead to judder. Much better is the Google Chromecast with Google TV, which also supports Dolby Vision, or the Nvidia Shield, which has enough power for everything.
Resolution 16:9 or 17:9 but also older Android version (?) for the most expensive! Maybe the most expensive is better for games and the cheapest enough for movies?