Yep, Rafa is playing pants at the moment, but remember he has only ever lost 1 match at Roland Garros in 10 years. The Philippe Chatrier Court is also huge and allows Rafa to stand a lot deeper to retrieve balls, which makes him that much more difficult to pass; this tactic just has not worked in the lead up tournaments this year, where the space behind the baseline is a lot tighter. Also beating Rafa over 5 sets on clay is next to impossible. So, for me he's still the favourite, despite his recent form.
Djokovic is next in line, but he like many players who never won the French (McEnroe, Becker, Edberg, Sampras) is a bit too desperate to win it to complete his career slam. I think this has affected his performance in the last two years, when he's lost to Rafa on both occasions, despite beating him soundly in the masters 1000s leading up to it. If Rafa falters, then it is Novak's ***le to lose. I don't really rate any other contenders. Ferrer is a great clay court player, but will not beat Rafa or Novak at the French, Murray, despite winning two clay court tournaments (his first ***les on clay) is being hyped up by some in the British press as a contender, but I just don't see it. He maybe playing well on clay post wedding, but Roland Garros is a different matter. He will be saving his best for the grass in any case. Federer won't win and his best chance at a slam is at Wimbledon. The other good clay court players like Fognini and Almagro are just too flaky when it matters.
Still, hopefully the French players can rise to the occasion like Monfils, Gasquet (although he chokes too often) Tsonga and Simon.
On the women's side - Serena will again be favourite, with Sharapova and maybe Kvitova as challengers. Don't know who else, as don't really follow the women's game closely anymore since Steffi retired.
