I don't think Evans has a chance to win, but he has a chance to podium. He had a bad Tour last year, but he turned things around at the end of the year (Vuelta podium, Worlds winner). He seems more relaxed since he won the rainbow jersey and moved to BMC. I don't think he feels so much pressure, which seemed wear him down in prior years.
Barring injury or sickness, Contador will most likely win. That leaves Schleck and Armstrong from last year's podium. I think Schleck could be passed for two reasons. (1) He's been battling a knee injury this year and so far he hasn't looked good at all. There's still a lot of time until July, but it's something that could be a factor. (2) He is the one guy who I think is willing to try to attack Contador and try whatever it takes to win. All he would have to do is push it too far on one stage and he could lose a lot of time while guys like Armstrong and Evans are doing the equivalent of a GC autobus.
Then there's Armstrong. I could see Armstrong on the podium again, but at this point in his career Evans is a better climber and a better TTer, so he has a shot.