There is really no difference between them, and all that matters are the raw materials used to produce them. Then, in the end of the day, the only difference is that some powder is pressed into tabs, and other powder is not. Personally, the only difference I see is convenience - it is much more confortable to take a pill or two before working out, rather than mixing the powder in water. Personally, I use DSpark, as it comes in pills, and it has no stims in it. Yet it gives me very good energy levels during training without th side effects associated to stim based preworkout supplements.