I think the ATP is too predictable.
On hard courts, grass courts, indoors courts ... Federer always wins.
On clay courts, Nadal always wins.
Should Nadal actually have a good week on hard courts or grass, he beats Federer, but off clay they are move even. I think its 2-1 Nadal. On clay, Nadal leads like 4-0. So, that has a lot to do with it.
I think right now the WTA is very unpredictable. Anyone in the top 10 can win a title any given week. On clay you favor JHH and Mauresmo (outside Paris of course). On grass you favor Venus and Sharapova (Davenport and Serena). On hard courts though, I think it's any one's game. Given the fact that since the start of 2004 its been so wide spread at the majors is proof of this.
JHH - Myskina - Sharapova - Kuznetsova - Serena - JHH - Venus - Clijsters - Mauresmo - JHH
Only JHH is the repeat champ, and twice on clay. Its anyone's game, which makes it exciting to watch.