Actually, after playing through with Tifa a lot in the single battles (got her up to level 20 on the first day, IIRC), I was really disappointed with how long it took to get to her story mission, because I think she is incredibly fun to play.
And I used the old Dissidia 1 to 100 levelling against Exdeath when I started my actual playthrough (first one was just messing around with the systems). It is quite a bit harder now that he has better attacks (chaining blocks into ranged HP attacks and new abilities like Maelstrom) and a max HP over 9999, but I managed it anyway. Even on Maximum difficulty, Exdeath is nothing compared to the awesomeness that is Tifa. At level 18, he's a pushover. :)
She was the only one I used the quicklevelling on, and just because I had used her the most and already knew how to use her, and to see if the trick still worked. Which it does. I have the Replay here. Can't figure out how to upload it to the site though (seriously, what happened to the link options? :(), but I'll try putting it on YouTube in a minute.