bona fides here: diagnosed ADHD Inattentive Type, scripted Adderall, Modafinil; former long-term crystal meth user.
Therapeutically, Modafinil seemed to have the best effect in terms of increasing both my focus and cognition.
Adderall helped me work for hours and hours on a task, but definitely caused my memory to get a little shaky. Harder to move stuff into intermediate memory on Adderall, so journal keeping was a must. But, able to work and work and work on Adds.
Meth combined obsessive focus with compulsive distractability, and almost certain brain damage. The period that I was on meth I look back on and feel as though I can tell my overall cognition decreased. Learning new things became harder, even though i was more driven than ever to obsess about any random topic.
All this said: I think the nootropics are the better class of drug, whereas stimulants mimic some of the effects of nootropics they feel neurotoxic. Modafinil is the closest to a nootropic drug amongst all these.
Have never taken piracetam, but have heard much praised heaped on this drug for increasing cognition and retention.
I'd go down that route.