A lot of it for me depends on what I can get at the time.
Based on the price or drugs in prison and on my on feigning scale, I say that nicotine is the most addictive. I almost completely gave up on cocaine long before nicotine. Crystal meth was not my favorite the first time I did it in 1997, but now it is my favorite--magia, magia, magica!!!! LSD is not addictive if they first time you took it you took four 300 ug hits. Shwee. MDMA was the MOST addictive substance I took until pills got weaker, semi-temporary tolerance set in and, now, I can't find 1/2 way decent pills. Temazepams are addictive if I eat > 150mg, but once they run out, I can take them or leave them. 2000mg of Depakote is a quite nice sleep aid, but I wouldn't call it addictive, only pleasurable. I have never been addicted to alcohol, although I did drink a bottle of Andre Extra Dry California Champagne by myself last night. I like hydrocodone and, to a lesser extent, codeine based cough syrups, but if I can't get those, then I like OTC cough syrup with doxylamine and dextromethorphan only. I once had many grams of pure DXM and it was wonderful until I flushed it. Mushrooms are not addictive unless combined with MDMA, which is a marvelous combination. However, they tend to grow on cow shit. Trazodone is just OK, but certainly not addictive. I didn't really get off that well on Adderall, maybe because I have always been used to good to very good quality crystal meth with more than 10mg (wtf?) per dose. I have never ingested Desoxyn, but there again, those pills are only 10mg. I hate Oxycontin, and I've only done it once. Hydrocodone pills were my favorite for a while but the constipation was *severe* when you eat THAT (90) many in 2 to 3 days. SSRI's are totatl bullshit. Adipex sucks. Wellbutrin is somewhat effective in making nicotine cravings go away by making cigarette smoke taste bad, but other wise would have been better off had it been granted and N-methyl instead of a
N-tert-butyl group. Also, it needs to lose its benzylic ketone. bk amphetamines, while mildly interesting, cannot hold a candle to their amphetamine analogues. I really, really liked 4-OH-MiPT, but I ate 50 drops ($50 bucks worth) to enter that space. I like caffeine A LOT. I've only had pure MDA once and it was excellent but a tad speedy. TMA-2 and TMA-6 are inferior substitutes for LSD-025. And don't let me get even near the ketamine--it's nasty, mildly addictive and makes me nuttier than a fruitcake in no time flat for about 3 to 6 months. Cocaine and Ritalin have comedowns from the devil.
Smoking a gram or two of yellow, sticky, pasty cocaine freebase out of a straight shooter (preferably a metal straw or pyrex stem)with rinsed Brillo pad on the end opposite your moutn and the freebase on the Brillo pad is 100% EXCELLENT. The comeup is better than other forms of ingesting cocaine, and the comedown is much milder. The only time I got the real thing with respect to pure freebase cocaine (for free, no less) was marvelous; of course, I had been tweaking hardcore for 2 to 3 days prior. I made some great art.
I have snorted and IV'ed heroin less than 10 times I would say, and it's very sedating but I tend to sleep for about 22 hours after each section and you have to trust you dealer VERY much to be messing with that crap. Otherwise, you might get a 'hot shot.'
Never smoked it though. Overall, real opium and 15mg at a time hydrocodone are my fav opiates.