The cleanest, can be costly from a price perspective. But the two that I know that are clean, use no fillers and proprietary blend free formulas are Up-Lift from Beverly International (Creatine and Stim free) and Bulldozer XL5000 (contains Creatine and BCAAs) from NRG. Another basic one is CGT-10 from Optimum Nutrition. CLOUT from MAN is also proprietary blend free, but honeslty I didn't like the results much. I think if you can afford one of these, get either Bulldozer XL5000 or Up-Lift. Otherwise just make your own mix.