I guess that's one reason why I'm not interested in Tifa... Fist fighters are typically boring, with very rare exceptions. Her style and limits have never been that interesting and as fist fighters go, she's one of the least impressive. Her boobs have more character than she does, honestly.
As for Vaan... really? I couldn't grasp him as the main character. He just doesn't fit it to me. Him and PeneloPE seem like they are tacked on more than anything. You could easily have the story without them or put placements to fill their positions with a few exceptions. Granted I never BEAT the game, but I played enough to realize Vaan really... was just there. The only person more transparent than Vaan was Penelo and she's actually MORE interesting than he is.
Oh well...
Final Fantasy XI has plenty of great characters in it, so there is a lot they could do there, like how they picked the awesome Shantotto. Stellar choice really.
Eh, I'm biased either way... but honestly, all people are, since everyone has an opinion. So eh.