I asked a question similar to this one once before, though it was not phrased as directly.
I would defo pick face.... I'm not hung up on big breasts so a lot of girls who don't have "great" bods can look a whole lot better with eating better and doing some exercise.... ie. they can improve what they've got. You can't do the same with a face, except with maybe piling on the makeup, but I don't really like that either. So a pretty face is the way to go.