Very difficult to quantify this is.
If I were to choosed based on which team I think will win it the highest % of the time you go with Astana, only by virtue of Contador, but not because they're the best 'team,' they just have the best frontman, although they'll have a perfectly good team if Navarro, Tiralongo, Pereiro and Vino all show up and are prepared to work for him.
If the question is which team has the best 'supporting cast' for their leader I'd say Saxo. Assuming Schleck the Younger leads, they'll have the strongest #2 man in Schleck the Elder, they'll have some outstanding 'mountain men' in Chris Anker Sorensen and Fuglsang, and a couple of guys who can really work the peleton with The Canc, Larsson and Voigt. Saxo have shown in the past that they can run really well as a team and everyone performs their roles well and without a fuss.
If you want to go for the team with the most GC talent you pick Liquigas; Nibali, Pellizotti, Basso and Kreuziger, all of whom will reportedly be at the Tour. No team has that amount of talent in the GC department.
There is also door number 4, which is which team is best equipped to achieve their own aims at the Tour, and that could arguably be said to be Columbia-HTC. They want stages, and with Cav and Greipel they'll probably win every finish without a significant incline. Also they have a pretty intruiging card to play for the GC in Tony Martin, who could definitely do something big, and anything he gets would just be gravy on top of Cavs' wins.