You've skipped over nicotine. While I've never smoked and could not recommend it (for many reasons) I do use nicotine patches for increased focus and productivity. Nicotine carries a lot of negative associations because of their link to cigarettes but a lot of the dangers of cigarette smoking are actually related to things other than the nicotine itself. The chemicals in a cigarette are quite toxic and cigarette smoke is harmful to the lungs. The fact that cigarettes co-administer MAOI's and have a powerful behavioural trigger that reinforces addiction makes me consider nicotine patches to probably have a low potential for addiction. On the stimulant angle, I also prefer the extended release stimulants, a slower release profile is much less spiky, and lends itself to a smoother experience, less tolerance and less anxiety.