I am not sure if this one counts but I found Sephiroth from Kingdom Hearts II really head, even at level 70 you are just starting to get into the level range where you might consider trying your luck.

If that doesn't count since it isn't a pure RPG then I would have to go with Seymour Flux from FFX (only cause I haven't played the International version)

I would have to say that FFVI was the best in the series if you had to pick one clear cut one.  It had the best story and character development of any in the series, and on top of that it had 14 main playable characters and even more that you had to play than just those 14.  For any game to juggle 14 different characters and have deep and compelling stories in any time period of video gaming is a feat on it's own.  FFVI has arguably the best villian as well in the series, Kefka is sick and twisted in his actions that is rarely seen in the franchise. 

FF VII's battle system and leveling system is all the advance forms of the magicite system in this game and the desperation attacks there are the snes version of limit breaks.   Any FF game between 7-10 (possibly more) would not have been the same without FFVI.