The Acetyl version is easily absorbed and ready to be utilized by the body without food whereas the other types are more effective when taken with a meal containing high GI carbohydrates and protein (or a protein shake with something like dextrose in it). I only have the Acetyl version right now and I'm taking it before my workouts with an energy drink (energy drinks don't contain enough L-Carnitine by themselves but have lots of caffeine). I also take it with my carb meals post workout.