We all like the 616 universe and everything in it, but sometimes we need some fresh air, and that's what alternate universes are for. Which is the best one for you?

To keep it interesting, let's focus on significant alternate universes (with an ongoing series or several set in it, revisited several times, etc.), not the ones used for a single story and then forgotten, such as those "What if...?" ones. But if it is a crossover with many tie-in comics to explore the new reality, such as House of M or Age of Apocalypse, then it's fine.

And now that we're at it, let's include alternate timelines and/or futures in it, with the same rules. The basic idea is the same: a new setting where things happen, and where some characters may move from and to on occasion. In fact, it's sometimes confusing if a given setting if one or the other.