Definitely weed. I have liked being slightly drunk and having sex, but my best ever was probably a 69 session on pot. Lasted a long time, felt really good, etc...
Most of these drugs I haven't done... I've heard about stimulants and sex, and I know the time I took a bunch of ephedrine and drank I was all dressed up and nowhere to go. I should have just jumped on the other guy's girlfriend who was dancing with me I guess, but eh, I was young and had morals...
Acid made me more likely to reproduce by spores than have sex, as I recall, though shrooms didn't dampen my libido.
By the way, after you quit doing crack its normal for everything to suck for a long time. Learned that in rehab...
Tim.