Mainly want to use in 3 separate offices and control the TV's remotely. Got pi 3 but its requires a lot of attention and work to get right. Android has the features I need, just need smooth playback on HD videos and mostly loop through them. A device that can stay on for months without a problem.
What about an Asus Chromebit on Chrome OS ?
Use RiseVision on a PI, i'm sure they also have a AndroidTV Client. I haven't looked though.
I'd probably say a nexus player would be fine for what you're looking for.
Refurb nexus players are available for less than $80 each. The only issues I know of are some h265 videos have issues but in a normal workplace that isn't an issue youll have.
It does 1080p via WiFi on wireless N or you can get an Ethernet USB adaptor.
Mine have been left on for months problem free, and zero sleep of deaths.
Here is a link that may help. It's an older article, but the software suggestions are still around.
For digital signage, a Rasp Pi should work wonders. You can remote into it, it can open webpages, it can do a slideshow.
Anything with Android TV is probably going to require a specialized app, unless you're just casting (which isn't as reliable over the span of "months") where a Chromecast would be $35 or less.
Again, looping a video file stored on a Pi should run forever. Having to repeatedly cast or loop on ATV would seem much more cumbersome.