I think Wiggo has a good chance of top five and outside chance of podium. My major doubt is the climate. I'm not sure how Brad handles the heat and mountains and there is talk of a major heat wave during the Tour. I think Sky have come on leaps and bounds and do think they have what it takes to support BW properly this year. Lack of climbing support could also be a problem for Brad though to be fair, if he is only thinking of podium he can use other contenders and their teams for support.
Green - I have doubts about both Cav and Husovd. I think they both have team problems that could deny them. Thor has Farrar on his team looking for wins and HTC have said that they have a 2 prong attack with Cav and Goss, which I suspect could well come down to a split in the ranks as Cav is off to pastures new (please not Sky but I know it will be. Couldn't Leopard REALLY use a sprinter?). I haven't read the rule changes for the green so can't comment on how it effects chances. I think team dynamics are going to be the problem for TH and MC. I wouldn't be surprised if it was an "unknown" taking it.
Yellow - I can't see Contador not taking it and the Schlecks making a cock up and ruining each others chances while they try to work for each other.
Polka Dot - Nibali if he realises he's got no chance of yellow and switches to going for Polka Dot. If not -no idea.