best euphoria is a nice big shot of heroin when you're dopesick out of your mind. Stick it, pull back, see blood, slam it then your body feels like a coffee cup being filled up with hot coffee or tea on a miserably cold day. That taste of dope in your mouth and then an itch creeps up your neck and all over your face.
^^I gotta say it's much more euphoric when your sick.
Speed balls are euphoric, well in the short term anyway. IV coke is fun for about 20-30 seconds a shot.
IMO my picks for most euphoric are benzos, LSD, and MDMA.
LSD+MDMA to get spun, plenty of benzos to chill the fuck out afterwards.