It depends. If you watch mostly 720p content, it will look better on a 720p screen.
If you mostly watch 1080p content, use a 1080p screen, simple. Avoid scaling whenever you can.
Or get a 4K tv, that can display both 720p (3x3) and 1080p (2x2) without scaling artifacts.
Too bad 900p won't look right on any of them :/







