This is a hard to answer question, because the answer is weed, but i dont consider weed a drug.
Weed and alcohol are the only drugs i still do, but i have done my share. So i'll say, BEST HIGH is either MDMA, Heroin, LSD, or Shrooms, or some mind bending Sativa from the volcano. MDMA is crazy expensive, and addictive, and dangerous. Heroin is cheap, but very very addictive, and can cause death. LSD and shrooms are only to be used when the setting is just right. Alcohol leaves you with a hangover, and makes you feel sick the next day. It is also potentially deadly.
But the best overall, if you include safety of use, lack of hangover, lack of addictive qualities, and quality of high, Weed is the ONLY one that could take that number one spot. Nothing comes close to beating weed when all factors are considered. That's why its the only one i can still do as i get up in years.