The odds of an X-Men/Harry Potter crossover are slim to none, but if Professor X's cadre of mutant companions were ever to enter the Great Hall at Hogwarts School of Witchcraft and Wizardry, listen to Dumbledore say, "Nitwit! Blubber! Oddment! Tweak!" and get sorted into their Hogwarts Houses, we're pretty sure we know which dormitory each character would be sleeping in that night--not to mention who would be Head Boy by the end of his years (ahem, we're looking at you, Scott).
There would be much more to worry about if the X-Men had magical powers (not to mention O.W.L.S. and N.E.W.T.S. to worry about) than which Houses they'd be sorted into, but at least we'd know which Head of House to approach if we saw Wolverine prowling into the Forbidden Forest at night, or Gambit sneaking off to the girls' dormitories.
Wolverine: Gryffindor
Who barges in, teeth and adamantium claws bared, before asking questions? Wolverine. While it's true that Logan is one to use his mind on occasion, literally sniffing out clues and following rabbit trails to solve many a mystery, including his own identity, that temper of his almost always gets the best of him.
Wolverine also has some Slytherin traits, like being ruthless enough to take out a child when it has to be done yet no one else is willing to do it. But his unabashed disdain for the rules, need to use up all of that aggression and complete fearlessness make him a Gryffindor. That does make us wonder if the Sorting Hat might choose otherwise if he didn't have his healing factor...
Gambit: Slytherin
The crafty Cajun who comes from the Thieves' Guild of New Orleans was raised to be a Slytherin. Like Draco Malfoy, he may have grown up differently had he been raised elsewhere and not been kidnapped and raised as a tribute to the Antiquary. Gambit is always looking out for number one, because he's always had to, and he hasn't always been the best teammate because of that fact.
Gambit's also willing to literally take gambits on things that benefit him, a recklessness that does venture into Gryffindor territory until you notice that these are calculated, self-serving risks, not acts of bravery. Case in point? Making out with Rogue.
Jean Grey: Ravenclaw
The Sorting Hat would definitely have a hard time with Jean Grey, particularly if she were in one of her many incarnations or the Phoenix form, which often changes her as a person. As brave, loyal and fair play-oriented as Jean has often been, she's also not-been these things, particularly in more recent versions of the superhero, and would definitely be sorted into Slytherin in some of these instances.
Jean has, however, always utilized her keen mind, whether it was literally in terms of telekinesis and telepathy, or while attempting to learn her powers, analyze the situation and make sense of things before she acts. While she's still rash on occasion, even as teen Jean she still made decisions--often quick ones--after attempting to gather as much knowledge as possible (even if that meant invading her friends' privacy).
Storm: Ravenclaw
While Storm definitely has traits from all four Hogwarts Houses, Ororo would best fit in Professor Flitwick's House. She isn't only intelligent on a general intellectual level; the Ravenclaw has great wisdom and is often the counsel that other X-Men seek when they need a sagacious opinion. Storm relies on her life experiences as well as her reasoning abilities to provide others, as well as herself, with the most carefully weighed opinion.
Storm has also had versions of herself in numerous universes that could be sorted into Gryffindor or Slytherin, particularly when she's fired up with power. Her loyalty to the X-Men over her own husband, T'Challa, also gives her Hufflepuff qualities.
Jubilee: Gryffindor
It's no wonder that Jubilee has looked to Logan as her mentor, given how much she, too, abhors rules and outdated regulations. She has always been one of the most headstrong X-Men and is one of the most likely to jump both feet into a skirmish without fully thinking it through.
In the past, much of this has been blamed on Jubilation Lee's youth, but even newer incarnations of the character, like Wondra, have had their wild and impulsive moments. She'll charge in to save someone even if she's fearful of the situation, which she's often done, and she hates being left out of the action.
Iceman: Hufflepuff
While the X-Men have definitely had their share of personality changes over the years, particularly when being thrown into an alternate universe, Iceman is quite often the happy-go-lucky guy who cracks jokes, helps hold the team together and is all about fairness. Even his first use of his powers on a bully was about doing what he thought was right in the moment.
Even when Loki messes with Iceman's powers, Bobby is patient and tries to be fair, wearing a power-dampening belt to ensure that no one gets hurt on his watch. He's one of the most accepting X-Men of other people, and recently he was revealed to be one of the few gay X-Men as well. Sure, during his second mutation he traveled into Slytherin territory, but he's generally been the Cedric Diggory of the group.
Beast: Ravenclaw
Of course Hank McCoy is a Ravenclaw. If Bobby is the team's Cedric, then Henry is certainly Hermione Granger. We're pretty sure he could pull that off for one of the Marvel Halloween cards, blue or not. Beast has some of the sharpest mental skills of any of the X-Men, a true scientific mind that sometimes gets him into trouble because he just wants to test the extent of what he's able to do, even when it's not the best idea.
The pursuit of knowledge is always of the utmost importance to Hank, even beyond Professor X's mission or any other goal. He's had his more feral years, but in general Beast is an intellectual before an actual beast. Hank would much rather be in his lab than out in the field, although he has spent some time behind bars protesting injustice as well.
Rogue: Gryffindor
It takes a brave heart to come back from being not only a villain but a villain who destroyed another superhero and absorbed her consciousness and powers to seek both forgiveness and a place to call home. Rogue has had to be incredibly brave her entire life due to her powers, but absorbing Ms. Marvel's strength certainly added a reckless fearlessness to her personality.
Rogue also has the qualities of a Hufflepuff, since she values fair play and loyalty, which is why she and Remy have butted heads so often over the years. But ultimately the one hero who can truly take on the Juggernaut has to be a Gryffindor.
Professor X: Slytherin
Even those who lead with good intentions often have their own agendas deep down, and Charles Xavier is one such person. Whether he believed in unifying mutants and people or not, he always had secret plans that, while Cyclops was happy to execute, many of his students found suspect.
Who else married Mystique, lusted after his own student (Jean) when she was young, had a secret child he completely neglected, often manipulated his students for his own gain or what he believed to be the best good without giving them a choice? In many ways, Professor X is the Dumbledore of the X-Men, and both men's cunning nature, often at the expense of others, should have landed them into the Slytherin House.
Cyclops: Hufflepuff
Scott Summers has, throughout most of his history, been the golden boy of the X-Men, eager to please his professor, carry out missions exactly as ordered and maintain loyalty above all else. He's a patient man, in most cases (with the exception of his relationships), and he values fairness and friendship--again, most of the time!
Of course, in later issues, Scott has shown many more Slytherin tendencies, but most characters go through arcs like that. He's left Wolverine for dead, made out on Jean's grave and done other heinous acts, but he'll always have that golden boy rep that he's had since he was "Slim" Summers.