For the next two seasons or so, I'd take KG. He is in a different stratosphere than Big Al in terms of defense, and he's also significantly better at passing, stretching the floor, and leadership.
Obviously, in the future, you'd want Big Al, because KG's skills have begun to decline ever so slightly from their peak. He's on the downside of his prime.
However, if a team needed a power forward to help them "win now", I think just about every team, universally, would take KG.