I haven't watched Naruto or Fairy Tail, but out of the remaining choices I'll pick Ichigo Kurosaki, as much flak as he gets.
Based on what I had read about Bleach, I thought Ichigo sounded more like dumb muscle than a main character. And while that might not be...entirely unfair, I ended up liking him a lot more than I thought I would. What I like about him is that at his core, Ichigo is a guy who's just trying to do the right thing. I think this particularly works because he constrasts well with the more morally ambiguous characters in the series. Beneath the scowl, the jerky tendencies, he just wants to be a good person.
Another reason I like him is that he racks up major woobie points during the series. I feel Ichigo doesn't have the same level of determination that so many other shonen leads do. He doesn't deal with failure well, and there have been a couple of points where he's entirely given up. Perhaps it could be accused of being nothing more than cheap angst, but I feel that it humanizes him in a way that doesn't usually happen to other shonen protagonists. I like determined characters, but I think determination becomes more meaningful if a character has limits, instead of just shrugging off whatever the plot throws at them. While it's something that could've been done better throughout the series, I think of Ichigo as a guy who needs the support of his friends to be successful even if he'd like to go it alone. He needs someone to pick him up when things get too heavy.
And yet, as much as I like him, I can't really disagree with most of the usual criticisms he gets. He does gain power too easily, he does have a history of fighting harder instead of smarter. Perhaps the difference between me and everyone else is is that I blame the writer for not handling his character correctly, instead of feeling that the character himself is the problem. And I realize you could probably do that with any character from any series, but I feel that Ichigo has a strong foundation.
I must say, I'm surprised that Naruto's gotten the least votes. I know he's controversial, but based on what I've heard about each of those characters, I would've expected him to beat Natsu and Ichigo.
