Favorite series of all time?

Hi Everyone!

In an effort to kick start this whole group I'm going to post an easy topic. What is your favorite series of all time? It could be a run of a long standing title by a specific writer, a limited series, or anything really.

This is really hard for me since I follow so many things so I'm going to mention some of my favorites, past and present, since I fail at choosing one.

I recently read it again and couldn't get over how amazing it was. House of M had amazing art, a wonderfully crafted story, and it just had so many amazing moments that really developed even further characters that had been a part of the Marvel universe for decades that you can't help but appreciate it.

Astonishing X-Men. Nevermind that it was written by one of my favorite people of all time, Joss Whedon, but the art was fantastic, the stories were unique and compelling, and they even threw in some funny moments to spice things up.

I have others, many others, but since these were the first two that came to mind I'm going to leave it at this for now. Anyone else care to share?