Sampras, Federer, McEnroe, Becker, Lendl, and Edberg.
Connors, Borg, Wilander, Agassi, Hewitt, and Roddick. Nuff said.
There's a reason why Sampras switched from a two-hander to a one-hander, and it wasn't because his coach thought it would make him a better baseliner (win the French). The whole point was to develop an all court game (win Wimbledon).
The two-hander is better for returning and it has some advantages on the baseline in general, but the one-hander has a lot of advantages also. It seems to help people develop a better transition and net game. Most two-handers don't have a good slice. Overall I don't think a two-hander is "better." A two-hander might be of greater benefit on the baseline, but a one-hander seems to improve the player in ways that the two-handed backhand just doesn't.
Personally, I could never hit a two-hander for the life of me. I can't hula hoop either. For some reason I think these two inabilities are related.