KG vs. Dirk is arguable. Let's break it down:
Scoring: Dirk. Dirk is/was basically unguardable. Can take you off the dribble, shoot over the top, possible the best faceup game for any big in NBA history. He even learned to start banging in the post once Avery got ahold of him. KG was no slouch as a scorer either, but his lack of a go-to move and tendency to defer/wilt in the 4th quarters of big games costs him major points here. His mid-range game was amazing, could take guys off the dribble, and had a sweet turnaround, but his post game was never as refined as it could have been, and too often he settled for those fadeaway jumpers.
Passing: KG. Garnett is one of the best passing bigs ever. His assist numbers in his prime were gaudy, especially when you consider his less-than-stellar supporting cast. Dirk is an underrated passer, and he eventually became quite adept at kicking it out of a double team, but KG edges him in this category.
Rebounding: KG. Not that close. Not much to argue here either. Neither player is a particularly incredible rebounder, technically speaking, but KG's prime numbers speak for themselves. Dirk always seemed to step up his rebounding in the playoffs, but I think people here forget that KG led the league in rebounding for a few years in his prime
Defense: KG. No explanation necessary. Anyone with eyes who watched NBA basketball for the last 15 or so years should know this.
Intangibles/leadership Wash. Although he behaves like a madman on the court, KG is a fantastic leader who has always been highly revered by his teammates. While Dirk is not quite the leader KG is, he's definitely the guy you want with the ball with the game on the line. Dirk always seems to make the right play in the 4th quarter, and aside from one playoff series, he's shown time and time again that he is willing and able to step up his game and deliver when his team needs it most.
Overall: Both guys have incomplete games to a certain extent, and both were able to win a le by having a player alongside them who covered up their flaws (Tyson to cover Dirk's ass on defense; Pierce and Allen to bail KG out in 4th quarters). KG is the more complete player, but I'm personally going to give the nod to Dirk simply because his type of offensive ability at that size is one in a million. With Dirk all you need is a defensive big next to him and you're instantly a playoff team, but KG requires a go-to scorer on his team, and those guys are much harder to come by. I actually consider KG more like a Pippen type.