Ok I can't compare all the games since I've only beaten VII and IX, but I vote for Safer Sephiroth (or however you spell it...) since FFVII was my first Final Fantasy, I never even worked out how to set their limit levels above level 1 the entire game through, and I beat it in about 45 hours which I think is pretty quick for me, since FFIX took me 91, and at 67 in FFX so far not completed.

Plus I beat Safer Sephiroth with my characters around level 50, level 1 limits, I was inexperienced with FF, I didn't have knights of the round, or mime or anything that I hear people always talking about. And I beat him first time. So he must have been pretty easy....or else I was just lucky :rolleyes2