When you go back to the early to mid 2000's no one had Dirk over Garnett. KG was the better passer, playmaker, rebounder, defender and while Dirk had an edge on him as a scorer, KG was no slouch. Dirk wasn't the dominant scorer that we saw in 2011 throughout his career. Before 2008 smaller players would routinely take him out of games just playing him man to man. I'm talking players that were 6'7 here. After the first round series vs the Warriors where Stephen Jackson locked down Dirk. Dirk worked on his face up and post up game in the off season and since then smaller players had no shot at guarding him.
There is no way in hell I'm taking any version of Dirk before 2008 over a prime KG, but if we are talking post 08 Dirk its tough. It would all depend on what my team needs. If I already have a go to scorer then I'm taking KG. If I already have a defensive anchor then I'm taking Dirk. Overall I would give the slight edge to KG because of his all around game.