X-Men 2099.
If your going to bring up X-Men 2099 you have to include their own version of the "junior" team. I actually liked the X-Nation kids, and wish Marvel would use them again someday.
In addition to some of the books mentioned here (especially X-Factor and Gambit) the first Adventures of Cyclops and Phoenix mini is a personal favourite of mine.
Quicksilver wasn't pulled from the book until several months after David had left. I believe Lobdell and J.M. DeMatteis were the X-Factor writers at that point and that Ralph Macchio was still the Avengers editor. (Brevoort took over around 97-98 when Busiek became writer.) Probably more relevant is that X-Men editor Bob Harras was writing Avengers and wanted Pietro back to play out the love triangle with Crystal and Black Knight.
But, yeah, David left because of the crossovers. The experience of coordinating X-Cutioner's Song left a bad taste in his mouth, and Fatal Attractions was coming just a few months later.
I loved Adventures of Cyclops and Phoenix. It is weird but is a very important part of the lives of Jean, Scott and Cable (maybe Rachel too)