Playing on clay will definitely be the big consideration for this match. Statistically speaking, Federer doesn't have what it takes to beat Nadal on it. Some people say it's just a matter of time and that Federer will eventually come out on top just because he's world number one. That's a bit of a stretch I think, quite a few number ones never took the French Open, Pete Sampras for example.

My money's on Nadal.