I had found some research, nothing definitive (what research ever is) comparing coffee to pure caffeine and it suggested that caffeine tabs work better than coffee. Pity's sugar free energy drink would proabably fall into the same categorie as tabs for the most part.
But there may be some reasons, if you want to get "big" not to use caffeine pre-workout. I am starting to realize that a lot more people use it for a "boost" than I thought and not just as a cutting stack.
Maybe time for a caffeine pros and cons thread.