A great feature to look out for is smart. This gives you access to all kinds of streaming and catch-up apps.
If you love sports or games, multi view will be your best friend. This lets you put your phone screen next to the action, so you can check your Twitter feed while keeping an eye on the ball, or play a YouTube tutorial to get through a tricky level in your game.
And if you just like things that make life easier, go for a TV with voice control.