It doesn't matter who (out of those listed) was the most powerful ever. Even if it did, then anyone here who voted someone other than Exar Kun is just demonstrating bias favoritism (especially those who religiously worship Revan).
"Grant Allen [...] had written a book about the Evolution of the Idea of God. [...] it would be much more interesting if God wrote a book about the evolution of the idea of Grant Allen." ~ G. K. Chesterton, The Everlasting Man