Rodman was the most versatile defender I've seen. In terms of defending power forwards, it's hard for me to say that he was better than KG or McHale. However, Rodman had the versatility to slide over and take SGs.
Of course, it's fair to argue that Rodman was so great at defense and rebounding because he expended zero energy on offense, a luxury that KG and McHale never had.
I think Pippen might have been just as, or more, versatile on D. PIppen could guard PGs and all but the bigger players at the 4/5 (he would have, it occurs to me, been even more versatile in today's game with all the stretch 4s).
And I think Pippen was phenomenal as both an individual and as a team defender. He was as good as Garnett, or very close, in terms of being able to guard his man and shut off another part of the play as it developed. I think Rodman was more of a man-to-man specialist.
And of course he also played an important role on offense, serving as a point forward of sorts. That's not about his D but, on your point, I think he might have been even more effective on D if he'd not been focusing on O too.