End of the day, I take a 'prime' Shaq over any other center, of any era. He couldn't be stopped. Kareem wouldn't be able to, and I'm not sure even Wilt/Russ could either.
Doesn't mean Shaq had the greatest career, but his peak was better than anyone else's.
Overall career success, I'd go Kareem, Russell, Shaq, Olajawon, Duncan, Chamberlain. I'm not including KG, he was a PF (and the best ever at that).