KG without a doubt.
Dirk is soft and one on one is a tough battle. Dirk would be flopping all over the place. KG is faster then Dirk, without a doubt.
Dirk can cover KG better then KG him? Dirk can't cover Tim Thomas let alone the former league MVP. KG is a all-defense team defender, Dirk is probably the worst starting PF defensively on a contending team.