I have to say San Antonio, and for a couple reasons.
#1 - they were a franchise-best 63-19 last year. If it wasn't for a fluke play by Dirk Nowitzki at the end of Game 7 of that series, they would have rolled Phoenix in the WCF just like they did the year before (and like they always do to Phoenix) and played Miami in the Finals.
#2 - IMO, they would have beaten Miami. The Heat and Mavs were both "Finals virgins" and had no experience on such a big stage. That might have contributed to Dallas blowing a 2-0 series lead and not being able to hold on to leads late in games at Miami. San Antonio would never, EVVVVER blow a 2-0 series lead to a team as inexperienced on that big stage like DWade and Miami were (at least as a team) or a double-digit lead in a game with less than 10 minutes left. If they do, I guarantee you that Gregg Popovich chokes one of his players not named Tim Duncan to death.
#3 - The games they lost to Dallas were pretty close. They nearly came back from the 3-1 deficit to beat them.
#4 - Not only were they 63-19, but they did so in a much stronger conference than the East. The East is now top-heavy, but in terms of depth, it is still horrible. The Kings were a very formidable 8th seed in the West and were a scare to knock the Spurs out, esp with Artest. In the East, it was Milwaukee as the 8th seed, and they were nothing more than a sacrificial lamb to Detroit.
So for those reasons, barring injury, I expect the Spurs to win 60 games again and try to get back to the Finals. They haven't won back-to-back rings yet, so I think that is their motivation under Popovich. Duncan still has at least three years left in him and is still the best PF in the NBA on BOTH sides of the ball.
