2005, and it's NOT close. The 2003 team was stacked, but moreso when we look at it in retrospect. That team had young, unproven guards on the wings in Manu and Tony, and a wildcard in Steven Jackson. Plus, Robinson was far past his prime. That team's chemistry wasn't near as good as '05--one only needs to look at the way they gave up so many leads late in games. People quickly forget that save for an out-of-nowhere performance from Steve Kerr, the '03 Spurs might well have been remembered for blowing a 3-1 lead against the Dirk-less Dallas Mavs in the WCF.
The '05 team, on the other hand, was a ing amoeba. Win slow and with D? Check. Win physical matchups? Check. Win playing uptempo? Check. It didn't matter how you played the '05 team, they'd beat you at your own ing game. Throw in the fact that the postseason run in '05 presented the toughest compe ion before or since (Denver, Seattle, Phoenix, and defending champ Detroit), and there's really no doubt in my mind that the '05 team was the best of the post-1999 le teams.