Creatine monohydrate is the form used in the vast majority of studies done and is a proven winner.
You’ve probably noticed, though, that the marketing machines of supplement companies are constantly pumping up fancy-sounding stuff like creatine citrate, creatine ethyl ester, liquid creatine, creatine nitrate, buffered creatine, creatine hydrochloride, and others.
These variations are certainly more expensive than creatine monohydrate, but studies show they’re no more effective.