I've played a good chunk of XII, finished VII, nearly finished X (nearly finished it twice - but never actually finished!), and am presently near the end of VIII. Keeping in mind that it's been a while since I played 10 and 12, I would have to say Squall. I really like him as a character, though he softens up a bit too much at times - when trying to get Rinoa back, for example. I also don't enjoy how he's pushed into the spotlight as the 'leader' at times. Cloud in FF7 had the excuse of being ex-SOLDIER (well...); Squall is just a SeeD like any other, except for his use of the gunblade and his talent. The latter's great, but when combined with his uncaring attitude it doesn't make for the most charismatic and likely leader.
But Squall's personality, otherwise? Love it - especially that whole uncaring thing I mentioned earlier. Even though it's humorous how he's pushed into these leadership roles he doesn't want, it's still not the most realistic use of plot device.