the players with the games (atm) to win RG are: Vaidisova, Mauresmo, Schnyder.
But these 3 players are mentally weak and I wouldn't bet on them in a tight situation in the later rounds of RG. Especially Mauresmo and Schnyder! Vaidisova is still unproven and she tends to lose her temper very easily and she hasn't played all clay season.
So I voted for the only past champions who have had decent success @ RG. Venus Williams & Elena Dementieva.