Our latest little film-playing box is a Nexus Player. It's good.
We have it connected to an Epson 1920×1080 projector and a Musical Fidelity amplifier.
The most remarkable features of the Nexus Player are that its remote control is simple and does not require line of sight, and that as of Android 6.0.1 it supports USB audio. Our amplifier happens to have USB input, so we get really good sound quality when we watch films.
Compared to the Popcorn Hour A-300 that's also connected to the same projector and amplifier, the Nexus Player has a real selection of apps and a much less confusing remote control. The A-300 can do better upscaling given the right video source, though, and has better support for playing from a local NAS.
Compared to the Roku 3 we have stopped using, the Nexus Player has better apps and no advertising. Roku really, really wants to display advertising to its paying customers. The Nexus Player (unlike the Roku 3) has a few annoying preinstalled apps, but it's possible to uninstall or disable all of those, and ours currently runs only Mubi and Plex.