I think it should possibly be retired for the 2005 run by itself. Made AI put up lousy numbers in round one, made Ray Allen cry in round 2, made Shawn Marion flat DISAPPEAR in the WCF, and then did a very credible job on Rip Hamilton before being switched onto Billups (who was murdering the Spurs up to that point) which was probably the key adjustment to winning the Finals.
If they handed out MVP's for the entire playoff run and not just the Finals, he might have gotten my vote that year. Throw in the defense he's played night in and night out, the big shots he's hit in the playoffs, and his dedication to the team as well as being a model for what it means to be a Spur, I don't see how this is up for debate.