The crossover event series has become the dominant business model for making superhero comics over the past 20 years and the X-Men are no exception. Line-wide events are a great opportunity to make a big splash in the market, allowing for new readers to jump onto an event that might change everything or giving lapsed readers an opportunity to fall in love all over again.

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At their best, the X-Men's crossovers have left indelible marks on the characters we love or give us exciting new worlds to imagine. At their worst, they ruin our childhoods. Not really, though. The bad ones just get forgotten...until now.

10 BEST: House of M

Avengers and the X-Men in House of M

Ever since Days Of Future Past, some of the most exciting X-Men stories show us the team in an alternate future. However, unlike the horrors of DOFP or Age of Apocalypse, Brian Bendis made mutants dominant, with Magneto lording over humans and mutants alike. The series was beautifully illustrated by Oliver Coipel and Esad Ribic's covers were striking and cinematic, but it was the Scarlet Witch's declaration of "No more mutants" that gave us the most iconic moment of the series and changed the X-Men's status quo while keeping their raison d'etre.

9 WORST: Trial Of Jean Gray

jean grey

This crossover between the Guardians of the Galaxy and the X-Men shares its core concept with Cosmic Ghost Rider. If you could go back in time and kill baby Hitler, would you? The Trial Of Jean Gray loses the fun of Frank Castle and Baby Thanos's space romp, with the Shi'ar putting a young adult Jean Gray on trial for the sins of her future self.

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In this context, punishing Jean for her future conduct feels more like 1984's Big Brother punishing thought-crime rather than the exploration of a philosophical question of how and when human nature is shaped.

8 BEST: Onslaught

Onslaught is literally the personification of the deepest, darkest parts of both men formulating into an entity so powerful that it took the X-Men, Fantastic Four, and Avengers to defeat him. On one hand, it gave Franklin Richards some well-needed attention as one of the world's most powerful mutants, but on the other, it gave us the short-lived Image Comics version of the Marvel Universe, Heroes Reborn.

7 WORST: Inhumans Vs. X-Men

Black Bolt leads the Inhumans while Magneto leads the mutants in a Marvel Comics battle

There is no escaping the fact that Marvel Comics is only one piece of a larger Marvel machine. Many of the ideas born out in comics go on to another life in cartoons, movies and other adaptions. In the years after the Inhumans movie was scrapped and months before the Inhumans television show would sputter out on ABC, this crossover event felt like the opposite approach. This crossover between the not-mutant-mutants and the mutants sees Emma Frost serving as the big bad in a war based on false pretenses and was supposed to serve as the starting point for new X-titles and new Inhumans comics. The reboot of the X-line after that was relatively short-lived, making this cross-over faded fast from memory and one that felt more like corporate synergy than ground-up storytelling.

6 BEST: Fall Of The Mutants

Fall Of The Mutants is one of the greatest crossover events in X-Men history and in Marvel Comics history. Chris Claremont's Uncanny X-Men and Louis Simonson's X-Force event gave us Senator Robert Kelly's Mutant Registration Act and Warren Worthington's reveal as Archangel. It also crossed over with Captain America, Fantastic Four, Hulk, Daredevil, and Power PackThis story was partially adapted in the X-Men cartoon and the first X-Men film, making it a part of the DNA of the team for even the most casual fans. It's a perfect example of how another story (Days of Future Past) can be a springboard for stories written years down the road.

5 WORST: Curse Of The Mutants

wolverine-curse-of-the-mutants-x-men

In this X-Men and Namor crossover, the team has relocated to San Francisco and Dracula's son explodes a blood bomb in Union Square which turns its victims, including Jubilee, into vampires. One would think that seeing Wolverine as a vampire (pictured above) would have put this crossover on the BEST list, but he's already a bloodthirsty berserker with pointy teeth, so we are left with an event that feels as disjointed as one might expect from a superhero/gothic romance story.

4 BEST: House Of X/Powers Of X

Xavier and Moira take center stage with the Krakoan era X-Men

Although it may be premature to name Jonathan Hickman's House of X and Powers of X reboot as one of the X-Men's best, there is no question that this line-wide reboot of the entire X-Men universe feels full of potential. If Days of Future Past could lay the seeds for great X-Men stories in only two issues, Hickman's 12 issue story which took place over thousands of years and many lifetimes feels like a nearly limitless breeding ground for future X-Men creators. So far, Dawn of X has been promising so we hope that we are living in one of the lifetimes where this crossover holds up.

3 WORST: Age of X

This X-Men Legacy and New Mutants crossover could have been the Age of Apocalypse for the 2010's. As you can see from the Oliver Copiel cover above and the Clay Mann art in New X-Mensome of the costume designs were as iconic as anything we had seen for the X-Men.

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Unfortunately, the ultimate conceit of the crossover lowered the stakes of the story within its boundaries. Alternate futures for the X-Men are best when they remain possible because future stories can be used as signposts to those events. Here, the Age of X lived and died with the whim of its creator, Legion.

2 BEST: Age Of Apocalypse

Joe Madureira's cover nearly says it all. We have Wolverine with a stainless steel stump. Buffed out Sabretooth with what appears to be a less-buffed out Sabretooth on a chain, bald Bishop, and a purple lady. The only thing missing is Fabio Cyclops. Age of Apocalypse showed us what would happen if Charles Xavier was dead and En Sabah Nur ruled the world. It was a dark time for humans, but a visually exciting crossover that allowed the creators to explore how different circumstances would have shaped the heroes and villains in the X-Men's world.

1 WORST: Avengers Vs. X-Men

Avengers vs X-Men

Civil War was one of the greatest crossover events because it took the safety versus security debate taking place in post-9/11 America and placed in a superhero context. The final fight between Tony Stark and Steve Rogers was heartbreaking and exciting. Steve McNiven's art was near perfect. Unfortunately, Avengers Vs. X-Men did not have a similar socio-political underpinning, with the belligerents seeming more like actual enemies than reluctant adversaries. The creation of the Pheonix Force Five diluted rather than heightened one of the most interesting and mysterious entities in the Marvel Universe.

NEXT: X-Men: The 5 Most Powerful Members (& The 5 Least Powerful)