I'd have to say the Adult Legion. While the Giffen/Bierbaum years seemed to have an almost sadistic feel to it, i.e. Dirk Morgana, Element Lad

(is he or isn't he?), the whole SW6 clone mess, it was really nice to see a mature Legion dealing with issues not only on a galactic scale but on personal ones. I did not agree with a lot of changes but it certainly presented more 3 dimensional characters vs. Golly Gee, let's try to beat Starfinger again. A few stories like 50 focused more on quiet contemplation and less on the huge action sequences.
Sadly, the whole End of Era situation felt rushed with a lot of dangling threads and to eliminate them, it was a simply a matter of causing a disappearance. The previous issues before 61 had built up an undertone of tension with Dawnstar's return. Both Wildfire and Dawnstar did not seem to know how to react. Given their history (this is a woman who suffered radiation burns for some physical contact), I would have like to see how that would have resolved vs. if the Legion will survive another Universo brainwashes the entire world scheme. And after some build up... how do they resolve it? Bang, Dawnstar "disappears" after issue 17 of Legionnaires.
Rereading it, I can only throw up my hands and shake my head. I can not say the whole thing was entirely callous, as Jo got a chance to say goodbye to Tinya but words can not convey the frustration as staring at blank page after blank page from issue 61.
As I mentioned in a previous thread, to chuck out 30 years of continuity and history seems a bit drastic and the new reboot does not seem to have gained a large audience outside of core fans. From what I understand, the demographic of the average comic fan is skewing much older i.e. past 20 if not 25 and any younger audience really seems to focus on the electronic media. Talking to a comic book shop owner, he mentioned that even given the popularity of some of the recent superhero movies, sales of comics for those superheroes has not gone up much if at all. The big sales numbers seem to increase when some big artist ala Jim Lee takes the reins for a few issues but then sales tend to subside afterwards.
I can only hope of an Elseworlds miniseries with a more Adult Legion vs. the Superboy's Legion miniseries.