For any gamblers, I think at those tournament odds Nadal and Wawrinka are both good bets.
Wawrinka obviously has a terrible record against Fed, but if he can somehow get through him, I'd like his chances against Nishikori or Tsonga in the Semi. Then for the Final, he's shown he can challenge and beat Nadal and Djokovic when the stakes are highest. I'm not saying he's likely to do all that, but for a 20:1 payout I think betting on him to win the tournament is a good wager.