Here is my thoughts on the main contenders for next year's TdF.
I can see Froome being very very hungry for the Tour, he has had a series of good GC placements (Heck 4th in this year's Vuelta if he achieves it is no mean feat, especially considering he rode arguably the hardest in this year's TdF). His Time Trialling I would judge to be roughly equivalent to Contador's , depending on the course - slightly better on a flat stage perhaps slightly less good on a hilly TT. Maybe he is slightly better with fresh legs but it is not a huge difference. His personal life seems well suited to the winter training as he has no kids as far as I am aware. His weaknesses may be a certain amount of tactical naivety as team leader that he has displayed in this year's Vuelta (Burning up domestiques too quickly) but I am sure Brailsford will talk about this with him if he gets the role of team captain at the TdF.
Wiggins - He clearly is the best GC contention Time Triallist in the world, even a crap winter training schedule won't change him probably winning next year's TDF time trial. Can he maintain his form for the mountains though, and will Sky make him the team leader or will they make Froome. Those are the big unknowns. Also, although hes clearly not 'off the rails' the man has enjoyed a (well earned) few drinks and smokes after his phenomenal success this year. There is also the issue of whether he can train as hard this winter and is prepared to miss his family and such. The parcours will of course have a bigger influence on Sky than anyone else since they will choose their captain based on it.
Contador - He is the best all round rider in the world at the moment. Weaknesses, I think he is probably ever so slightly weaker than Froome on a flat TT (If they are both fresh), he won't be as fast as Wiggins in the TT. His Saxo Team whilst strong, I don't think it is quite the same level as a full strength Sky team. He is going to be hungry to win more Tour De France, but will he also want to go for the Giro again ? If he focusses clearly on the TdF and there are enough hard mountain stages he probably will destroy the Sky Train in the mountains. Mentally his attacks put alot of pressure on a team captain as well as physically so if Wiggins found the 2012 Tour mentally tough, boy will he find it a hundred times harder if he is carrying an advantage from the Time trials into the mountains and being relentlessly attacked by Contador, obviously this applies to Froome too.
Schleck, the big unknown. He never seems to be fit at the moment for whatever reason and though he is obviously maybe the most talented climber in the world, I think he will lose way too much time in the Time Trials. He also has the weakest team of the main contenders. These factors mean that I don't think he can win the TdF.