Just speculation/opinion but I'd bet MD and Psylocybin are the most robust candidates. LSD and Ketamine have solid potential but I see those encountering more bumps in the road.... :D Any of them could have effective use cases, but the same risks are present with these substances, to an extent, that are present with the current pharmaceutical industry if it ever got to the point of distributing prescriptions instead of controlled therapy. I do see immense value in the possibility of replacing prescriptions with therapy for many people struggling with stress, anxiety, ptsd, ect.
I'd definitely like to see legalization over prescriptions, but as I said the whole therapy aspect is really cool.