What's your budget? The Walmart ones might be all you need. Do you really need it to be Android TV? I have both Roku and Google TV clients. I like the Roku one, but not a fan of the closed ecosystem (can't side load or adb).
You shouldn't need anything crazy to play your media, but if you go with Google/Android please replace the default launcher. You will very happy then lol.
You can sideload Roku devices. Hit a button combo on the remote and it enables developer mode and a web page you can upload the package to. It's been a long while since I've messed with it so I don't remember many specifics
The Walmart "onn." has been perfect in my household. Dirt cheap at $20, degooglable, good remote (you can use an app to rebind the streaming service buttons to apps you actually use). Supports the Google cast protocol and also SmartTubeNext. No ads of any kind on the home screen, because I'm using a custom FOSS launcher.
Yes, it's decent. Used one for almost 3 years, recently upgraded to shield pro and love it. You don't realize how slow the Chromecast is until it's compared to the shield pro.