But of the guys that I've seen play on your list - I would rank them this way:
Kareem
Shaq
Joker
Olajuwon
Ewing
Malone (assume you meant Moses, since you seemed to be focusing on centers)
You've left off a few others (David Robinson, Tim Duncan) that need to be considered too. If you throw in those guys, I would probably put Duncan just ahead of Joker at this point, but it's close.