So yea I love Marvel comics, been reading them since I was a kid. My two favorite crossover events of all time are 1) Secret Wars and 2) The Infinity Gauntlet. Those two are just so freaking epic and I pretty sure the Beyonder and Thanos (with his infinity gauntlet) are the two mightiest foes the heroes have ever faced. I've got the books from those 2 series and I've read them countless times over the years
But I'm sure there must some other cool ones out there that I've missed out on. So if you guys got any you'd like to recommend please do