This is going to depend entirely on the user, why they take the drug, and what tends to happen to them when they take the drug. A drug experience is a dynamic interaction between a person and a chemical. It's not just about what's in the pill.
If you're talking in generalities about statistical likelihoods, then I'd have to say L-theanine. It's legal, has a sky's-the-limit LD-50, no withdrawal, no unwanted side effects, probably neuroprotective, and gives a sharp, 'all shiny and new' mental effect that's great for either recreation or motivation. Does it have any of the treacly euphoric bliss of any of the 'hard drugs' or 'real drugs' 8) ? No. But I'd go out dancing on nothing but theanine and caffeine, and not expect the night out to be in any way lacking.
I'll boldly state that if a drug user is using any drug to numb the pain of their life, or to try to avoid facing or thinking about something painful, then their use of that drug is inherently unsafe, and if allowed to continue, will lead to serious problems.