iTunes 1080p video looks better, saves space using better H.264 compression

This is exactly the sort of article I was looking for. Also worth noting from this piece:

The 1080p version only plays on third-generation iPad and AppleTV, and the iPhone 4S.

So unless you only have this year’s devices, stick with 720p. If you have all new stuff 1080p looks a little bit better and the files aren’t much bigger.