Let's see:
From VII, there's got to be Cid. He's a tough old bastard. And really, he has one of my favorite lines in the entire game. In fact, it's one of the first things he says, and as soon as he said it, I thought to myself "okay Cid, you've officially won me over". That line? "Sit the fuck down and drink your fucking tea!". Poetry.
From X, I'm gonna be a HUGE bandwagon jumper and say Auron. How could I not? He's awesome. He checks off all the boxes on the badass list quite nicely. And, again, he has my favorite line in the game. Ahem:
"Now, this is it! Now is the time to choose! Die, and be free of pain, or live and fight your sorrows! Now is the time to shape your stories! Your fate is in your hands!". A motivational genius, that man.
And lastly, there's Sazh, from XIII. Admittedly, I still need to finish XIII, so this might not be fair, but I think Sazh was just really endearing, and stuck out to me, even while I was still playing.
Funny how all three of my choices are the "old grizzled bastards" from their respective games.