Bomani Jones has made the argument that in 2005, 2006, & 2007. Dirk was arguably the best player in the NBA and is criminally underrated as a result. His Win shares/48 during this period reflects this claim.
KG's inability to get Minnesota out of the first round sans a single time in 2004 tells me that there's no debate between Dirk and KG. KG played with Terrell Brandon, Tom Gugliotta, Malik Sealy, Sam Cassell, Stephon Marbury, Latrell Sprewell, Chauncey Billups, Isaiah Rider, Wally Szczerbiak, Joe Smith, and a number of quality NBA players yet did absolutely nothing with his teams when he was the lead dog. Go look at the rosters Dirk carried to the Finals in his 2 appearances there. From 2007 until Luka arrive Dirk only played with 2 other allstars, Josh Howard & Jason Kidd. Mark Cuban deserves a roster malpractice suit brought against him for how inept he's been at building rosters around star players.
In their sole playoff series against each other Dirk wiped the floor with Garnett averaging 33 and 16 rebs against him in route to a 3-0 sweep.