It's always hard for me to whittle down a definitive list for anything; I usually choose a "best of" listing, with explanations for each (it's just my nature of indecisiveness and never developing that "playing favourites" gene).
With that pre-face, I gotta go with:
1.) Gambit (Remy LeBeau) - He has more facets to his personality and mutant power acumen than initially-stated for the early portion of his comic's character birth. I admired his
Southern-gentleman persona and ideals, despite being associated with an organization named
The Guild of Thieves. His continued on/off relationship with
Rogue was always a highly-intriguing subplot, in my opinion. His mutant ability to charge any object's potential energy into a kinetic, volatile, and explosive projectile makes him highly versatile in terms of fighting capabilites. Additionally, he further learned how to charge his own body into a "fast-moving" near-concussive-like shielding. Despite being a mutant, he is a highly-specialized combatant, skilled immensely with a
Bo Staff. He has also been speculated to be one of the 10 strongest X-Men of all-time.
2.) Nightcrawler (Kurt Wagner) - A favourite character of mine nearly throughout the entire serialization of the comic, (and subsequent TV/film series) despite being an obvious minor character (he was usually reserved in background roles until the story warranted his prominence). But, besides rarely seeing the soft-spoken Bavarian orphan, he was beyond captivating. He definitely has my
favourite mutant power from the multitude of mutant variations featured in the entire Marvel Universe. What's more: He is an accomplished swordsman (dating back from his Circus-days as a fencer) and combines his natural deftness with his acrobatic abilities (along with a prehensile tail), and combined with his ability to teleport at will, Nightcrawler is a fierce fighter to square off against. Though, he would much prefer not to fight at all, as he is a natural pacificist more often than not, even so far as being a priest before (and after) his stints with the X-Men. *BAMF* What more do you need to say?
3.) Beast (Dr. Henry "Hank" McCoy) - I guess I have a "predilection" towards amiable and thoughtful, blue-furred, misunderstood, acrobatic, "beastly-looking" characters (must stem early-on from my affection towards the
Cookie Monster, tho I have no idea if he is nearly as agile). I suppose "Hank" appealed to my intellectual nature, first-and-foremost, for he was always quick-witted with words and even offered sound advice whenever he was featured. But he's also like the "Blue Hulk" in a way, what with his superhuman strength, stamina, & speed, (plus near-unmatched dexterity and agility) but with a more-preserved awareness and intellect when pressed into combat. This little excerpt most appropriately delves into the great personality that was bestowed upon his character, and why I so heavily-gravitated toward it:
Despite his ongoing battle with the demons of loneliness and rejection, he was an inveterate prankster and wit, and besides his brutish exterior, Beast was the most literate and eloquent of the X-Men, possessing a million-dollar vocabulary. Henry was every bit a human being plagued by duality: man/beast; genius/sports star; gentle giant/feral aggressor. From
Beast to "Best"; He has it all.