for me, nicotine is the one...maybe because of its availability...maybe because of the short time span between fixes (apparently body starts to crave again within 30 minutes)...interestingly, i once read that nearly 100% of heroin addicts are smokers too (think it was Allan Carr who said that?) also i believe people who smoke weed daily, but not cigarettes, are actually addicted to the tobacco...anyway, i've tried everything except hypnotherapy to quit the fags...that's next on my list...all my other vices are thankfully under control...