The thing about stims is that they don't form a physical addiction. You may have physical discomfort when you are activelly coming down from the stim, once you have gotten a good night of sleep and been fed, you'll physically be fine. Mentally, however stims can be VERY addictive. That mental dependence is what makes stims so addictive to some people. I think that it depends on the person too. I like stims, but once I'm out and manage to come down, I don't even want to think about stims for at least a couple of weeks. However, where as some people try opioids once, get dizzy and sick and never touch them again, the first time that I did opioids, I knew at once that this was something that made me feel at peace with the world. I've been battling the lure ever since. So, for me the most addictive drug would be opioids, more spec. heroin.
But, that's just me, and the answer will vary depending on the person.