Truthfully, as far as raw power Revan is around Yoda tier and people generally hold his raw DS incarnation from SWTOR's Shadow of Revan expansion as his most powerful, as it has the most impressive quantifiable feats. Namely rag-dolling the entire strike team (minus protag) sent against him to the point they were utterly helpless. If memory serves only intervention from his LS incarnation is arguably the only reason the team won.
Truthfully however, I have always wondered as to the validity of SoR Revan being his most powerful POSSIBLE incarnation. If I am not mistaken, when we see RR (Revan Reborn) perform he is doing so not only on a strong DS nexus (Wherein there are possible implications of hindrance but also ones for him being amped) but also without sleep and pretty terrible shape overall. Perhaps someone could jog my memory of the Revan novel about this? Never read it myself but one sees these things talked about enough you remember whether you want to or not.
Thus, to be a short and blunt as other answers have been and reiterate.
Yoda tier on raw power; Strongest version we see is SoR
I would very much appreciate if someone could clarify the above things for me though. I'm going off no sleep for a day so my memory isn't too clear right now.