For your question about best stimulant:
AMP is my favorite.
In old days, it'd be AMP + M5AA such as Methyl-Rage. that was the stack for beating personal bests. Not sure if there's a fast acting, fast clearing androgen that's otc anymore.
I think what you saw in the responses was people think of having a great workout in terms of:
Mental Focus, Sustained Energy, Stimulation, Recovery between sets, and Endurance for Volume of workouts. Depending on your routine you may need aerobic as well as anerobic help.
That's why music, carbs, BCAA's, Citrulline, stimulants such as AMP, ephedrine, and nootropics such as ALCAR, are mentioned.
For optimal workouts, you need enough sleep, and enough food in your in the day before and the hours before you workout. Then you take a stimulant like AMP, and you kick ass.
I know you probably know that, but too often people ask, "What stimulant should I take." And that's to counter that they dont have their act together in terms of nutrition and sleep.
With stims like AMP, in my experience, half of the effect is based on the quality of your sleep, rest, nutrition, etc. You cant take it routinely and expect great results, if your sleep and recuperation strategies suck.
Imagine stimulants are like drawing on your bank account of energy. If you dont restock your account with good sleep and eating and recuperation, eventually you'll get less and less effect. Avoid that and you get more from whatever stimulant you pick from what's out there.