The Nvidia Shield is probably your best bet on the least amount of crap on there that still gets regular updates. You can change the luancher to hide the ads and lock down as much of the phone home with Adguard.
Also when you look at majority of Android TV devices, none of them get any update. The only ones that seem to do are the Chromecast TV and Nvidia Shields. If you're in Murica, you can pickup the new Onn box for $20 but being that cheap it will probably be phoning home more.
End of the day you just want your TV to just work. If you start having to sideload Netflix/Prime/Hulu, you're gonna encounter sooner or later spending hours just to fix it.