In terms of a 1-12 roster, the Mavs are easily the better team, but when you have 2 superstars and and an all-star of a 3rd player and a bunch of spare parts around them, does not a team make.
If Miami wins this series it won't be because of Mike Miller or Mike Bibby or the host of spares they have at center. They will win because of the combo of Wade/LeBron/Bosh is just too much individual talent.
For the Mavs, you'll have Dirk, but your going to see contributions from 8-9 deep. To me that is a better team....but like it was mentioned elsewhere, sometime it doesn't matter when you have 2 of the best players in the world that can absolutely take over a game or a whole series.