My favorite pre workout powder does change from time to time, at least in terms of which specific brand, flavor, and variant it is. Having said that, the things and factors that determine my favorite from time to time do not change all that much.
I am a big believer in getting protein before exercising. I find that my body repairs and maintains its own tissue best when it is already digesting protein during the actual exercise. I feel like my body is more likely not to burn its own muscle mass for energy if it knows there is protein being digested. An actual doctor might dispute that, and maybe it is all in my head, but even as a placebo effect, it gives me confidence that my exercise is going to help my health.
Taste is a factor in determining what my favorite pre workout powder is. I do not want anything I might still be tasting in the middle of a workout, so I do not really do chocolates all that often. Vanilla flavors I like since they are easy to wash down. Strawberry flavors are not bad either.
Something else I like to see is volume pricing. I am a sucker for coupons, bulk discounts, or large containers that cost less per gram than their smaller cousins. I do usually have to factor in shipping into this, but a lot of sites offer free shipping for minimum orders of enough cost. Any site or store that does this earns a bookmark in my browser.
I also like powders that also have nutrients other than just protein. Powders are not like power bars I use after working out where you get almost all your RDA of many nutrients all in one, but anything helps.