I've heard these interesting claims that Nadal would be better since he leads in the matches between the two.
But then again, Nadal is a 6-time Grand Slam winner (4 in French open, 1 Australian open win, 1 Wimbledon win), which is great, but Rog Fed's stats don't lie: 16 Grand Slam wins (WR), 22 grand slam finals (WR), 23 consecutive Grand Slam semifinals(WR), and so on. Also, 4 ATP World Tour Finals titles, and an all-time record of 26 ATP World Tour Masters 1000 finals. Moreover, he's holds the record of most consecutive weeks as nr .1 player in the world, 237 weeks. And he's just 2 weeks away from Pete Sampra's all-time record of most weeks as nr.1 in career(286, Fed: 284). And he's got the most earnings of all tennis players.
So, you could say that Federer is a record-breaker, historically amazing player. Nadal might dominate in French Open, but Fed takes the other three...