DXM by a billion miles, but I did become a raging addict (and very quickly) so I gave that up.
Weed is number two, but by virtue of it's enhancement qualities. The real standard should be how fun it is in an empty room.
Hallucinogens paled next to DXM, so they aren't that great anymore.
Meth just made me stay up for days, I never really noticed much of a "high" to speak of.
Conversely, alcohol makes me fall asleep almost immediately.
I sniffed glue and it was ok, but felt bad for doing such a low rent, hillbilly drug.
(Those were in order)