I've got three nvidia Shield TVs, but not the newest model that supports the AI Upscaling and such. I wouldn't use anything else since they work so well for me. At this point almost every issue I had has been dealt with. It plays back everything without any issues. Especially stuff from Plex.
Plus, wife and kids have no problem using them.
The other option, but less powerful, is the Chromecast with Google TV. I've got one in my sons room, and the kid profile mode is awesome.