I liked them all, but nothing compares to the sheer sadistic madness of the Tomb of Horrors.
I also liked L1. But then it is hard to get past the nostalgia.
I am now looking back on fond memories of over a year ago when I ran the Sunless Citadel and Forge of Fury. I'm finally running a group though Speaker in Dreams, and that is also turning out to be quite fun. (IN the intervening time, i ran other adventures, and now this is a different group - but I will probably take then all the way through the remaining 3E modules to 20th level. Then my other group is tackling RttToEE - with my 60 hour weeks, I have no time to work up my own material anyway)