I have an AppleTV 4, a Roku 4, and Android TV is built into my 2015 Sony.
AppleTV is by far the most refined / stable.
Roku has a bit more content, but I find the remote locks up much more often.
The AndroidTV has the most content options (espsecially with Plex, etc), but is also by far the least stable.
I find I end up using the Android TV for Netflix and Amazon as thats the best way of getting 4K HDR.
I use my AppleTV for anything 1080p, and I use Beamer.app for streaming mp4/mkv to it (with transcoding disabled -- passthrough only to reduce compression artifacts).
The Roku 4 is in the guest bedroom -- the primary reason is the color decoder on it is VERY inaccurate, with a very noticeable 'red push'. The Roku 4 is the only electronic device I've bought in the last few years that I actually regretted buying.
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