Until about two weeks ago I would've said ketamine for sure, since I'm bad at ending a binge, even if that binge is countable in days instead of hours, with the longest one so far being 9 days but on average the binges usually aren't that long and if I used a few days in a row I'll take break for atleast one or two weeks and that usually goes fine too. It's on my mind a lot too, but if I'm not using it, or even if I run out and can't get any I feel fine, if not good. Mentally and physically I feel good on it ánd after it, not even just the week the antidepressive effects might last but longer too. Even if I take more then a two week break, from the first hour of not doing any to the day I do some again I feel good, just as good as I would've felt had I never done it, probably even better due to all the great memories, insights and art/music I made under influence (I paint and make music while on ketamine, and I still love those pieces when sober).
But weed.. I thought it wasn't as bad, but I smoked hash and weed daily the whole day for 6.5 years, and even though it was easier to just 'not do it' then it would've been with ketamine, I felt MUCH worse. No sleep, depression symptoms, no motivation or inspiration whatsoever; absolute horribleness mentally and bad insomnia, even on valium and metalonin which both normally make sleep seriously easy. Even 10 days after quitting weed I still feel not myself, I wasn't aware how intense it'd be, but I can easily say for me the most addictive ''psychedelic'' is weed / hash. It's easy enough to just quit, but the symptoms, they sure are there, especially mentally. I never felt bad after taking a break from any drug (never did any addictive drugs either though

), but this is properly messed up.
Classical psychedelics aren't really addictive, but the psychedelics I'm most likely to do more often then I planned ahead are magic mushrooms and 2c-b, robably because of the short duration. I bet if LSD lasted 4-8 hours as well I'd do that more easily too.