I'm gonna be the odd-ball and say 2-FA. When it comes to functionality, it's a wonder drug for me. I've tried speed, adderall, ritalin, and cocaine, and none of them come close to increasing my mental function as much as 2-FA. This is assuming I can also use other drugs (I've had only positive experiences mixing 2-FA with a variety of drugs). If I couldn't use any additional drugs, it'd probably either be a moderate weed high or the equivalent of 2mg of xanax with no tolerance. ~45mg morphine ER with no tolerance would be nice too.