One of the problems I think hurt the early book was that the X-Men graduated so early. What was it--in issue 6? 8? And presumably, they'd have been weaned off the Professor's input somewhat. Instead, nothing happened. The status quo didn't change a bit. They still hung around the mansion, doing basically nothing. The initial (and very good) threat of the Brotherhood was gone by issue eleven. Then they spent the rest of the 60s banging into each other, accomplishing nothing. If it weren't for the great final issues by Neil Adams, I don't think they'd have ever been successfully resurrected later on.

About X-Factor: it was probably my least favorite mutant book of all time. I absolutely hated it. The only reason I ever bought it was for the sheer novelty of having the original five X-Men back together again. The novelty ran out before the end of issue one. I hated the concept of the "mutant hunters" thing. Stupid, stupid, stupid. People used to make "Ghostbusters" jokes about that dumb concept. And I don't think the Simonsons added anything good to the mix. Most of the time I had no idea what was supposed to be going on in that book, and that's okay, because neither did the writers. All these mutant team spin-off books end up in the crapper anyway (Generation X, New Mutants, Excalibur...the list is endless. They always get screwed up somehow).