I'd rank Andy's chances as AO>Wimby>USO>FO. The surface at the Aussie Open really suits his game and he often plays great tennis there. He's had consistent results at Wimbledon (since 2008: QF>SF>SF>SF) and I'd like to see how he performs if he can draw someone other than Rafa in the semis this year. He's had mixed fortunes at the USO (since 2008: F>R4>R3>SF) which surprises me as he does generally play well in Canada and Cincinatti beforehand. It would be a huge surprise for Andy to win the French Open having never won a clay title before - there are several better claycourt players than him.
This year I'd say his best chances would be at Wimbledon. He always seems to serve well there which is good for his overall game. If he could play like he did against Novak in Australia then he'd have a great chance. He played aggressively against Rafa in the first set of their semi-final but unfortunately went back to a defensive gameplan after that.
Are there though? It's very hard to say where is on the clay right now. He beat everyone he came up against last year apart from Djokovic, Nadal (and a poor performance against Bellucci), and he pushed both of them very hard. The problem is, none of the players he beat last year were particularly high ranked, so it's hard to tell where he does rank in terms of clay court performance.
As has been said many times on here as well, Lendl was a great clay court player as well so you would think he would help Andy improve even further on this surface.
Next few weeks will give us a real guideline as to where Andy does stand on the clay - can he go further and beat one of the top three this time? Barcelona should be a great indicator, particularly if he draws someone like Berdych or Ferrer.
What's important for Andy is not to let himself get down from these defeats, continue to play more aggressively and hopefully continue to improve as he has under Lendl. If he does, he should be able to finally beat one of the top two in a Slam and go (at least) one further than he has in the last five Slams. The worry is that either he's focused too heavily on the SFs that he gets knocked out by someone else early on, or that when he does get there he plays like against Djokovic in Miami and gets a bit more passive.
I have a feeling this will be a defining year in Andy's career. Big, big year for him if he's ever going to win a Slam and prove to the world once and for all that he can compete with the top three.