All the Sony TVs have Android built in, and they make some of the best LED TVs, along with Samsung who use their own Tizen OS.
LG, who are the only ones making OLED tvs, use WebOS.
LED sets are brighter, so perhaps more suitable for watching in well lit situations, OLED sets have perfectly black blacks, making them better for watching movies with the lights down.
You won't be able to buy a 'dumb screen' at a TV sizes, but nobody is forcing you to plug an ethernet cable into it. By the time 4K content is more widely available, external HDMI 2.0 boxes should be cheaper.