I've worked out my whole life (since around age 14, now over 35) and had periods where I did a lot of supplements like creatine or pre-workout. I no longer bother with them, although creatine is one of the more well researched / "real" supplements, so you're better off with that than lots of others. To me though they've never really done anything (besides cost money). In my opinion the best bang for your buck is drin…
I know caffeine is detrimental to my workouts because it dehydrates me and raises my heart rate. I have clear personal data on this. Creatine is well established as a substance that has a real measurable positive impact on people.
I have the fast processing version, but those with the slow processing should avoid caffeine at all costs.