Out of the list, id say probably sidious
out of what i know, Nihilus was the most powerful force being to have ever existed in the SW universe. (i aint no nihilus fanboy. its just fact)
i hate caedus, but he was very powerful. more so than vader. (but thats not saying much
bane was very cool. i dont know about his power, but he is SO the sith'ari. no competition. i personally dont see how anyone can even argue otherwise.
revan was the man. most powerful in the kotor era second to nihilus i think.