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).
"There is something going on in time and space, and beyond time and space, which, whether we like it or not, spells duty." -Winston Churchill
"For of all sad words of tongue or pen, The saddest are these: 'It might have been!'" -John Whittier
"Apathy is death." -Kreia