It depends on your preference. I've rented both and I'm still pretty split. I think I may go with 2K3 because it more sim-like while Live is more arcade like. I don't think you could go wrong with either. JMO.
The only thing I hate about the Live series is that my player ratings almost never move from year to year in the game. Ive stayed at a lvl 91 Francis for 4 years worth in the franchise...