Which is odd since the Legion of Superheroes had rather strange looking characters already and they even developed more later on. Glad it didn't happen too. He is much more interesting as a mutant.
If anyone hasn't guessed yet:
Nightcrawler. He is visually striking and has a cool powerset, blending and seeing in the shadows combined with disappearing in the blink of an eye, climbing buildings, well you cant get honestly cooler than that. He loves his friends so much, he is loyal, passionate and idealistic.
As I said his pals are important and he has developed a protective older brother attitude toward Kitty.
And there is of course his bestest friend Logan who he didn't mind braving hell in the afterlife for to lend him a hand. Can't not mention Ororo and Piotr as well - the ANAD team plus Rachel and Kitty. I'll add Betsy, she's pretty close with him too. They bonded during the XSE and the Remender era.
And his passion, sometimes fiery, sometimes explodes when he feels there has been a major injustice. The beast gets unleashed!
He has a nice smile. The cheak bones and the nice little toosh doesn't hurt none either. :-p
I love the X-Men as a whole and think everyone has contributed something unique to the mythos. That said here are the runners up: Shadowcat, Psylocke and Wolverine... but the latter not as much these days with too many different interpretations and overexposure. I liked him best as the man with a mysterious and relative unknown history who struggled to be a man, the failed samurai. Oh, and Iceman is my favorite of the 05. Storms around there too in her "mohawk days" even if I like her in general.