Man that's a tough question. I love them all, it would be really hard to choose. It might be LSD. But LSD doesn't cover all the bases. It might be DOC, but the duration is too long. It might be mushrooms or 2C-E because they're both the deepest substances I've ever done (in different ways), but both are not that recreational for me and I only want to take them from time to time when I'm trying to trip with a purpose, and most of the time I trip these days it's just for fun and to sort of keep maintaining my connection to the joy of the little things/my inner child, rather than to trip balls, go deep and figure shit out.
PAWS from long-term opiate use lasts a long time and makes everything feel dull and flat. But it is possible to get out of it, just hard. I did ibogaine to get off opiates and it seemed like it dug the addiction right out, I came out of it feeling like I had woken up from a nightmare where I was insane, and I was sane again. I immediately went on to have the best 2 years of my adult life, no PAWS whatsoever. I wonder what it would have been like if I hadn't done ibogaine?