In my opinion, Cooler's not only my favorite Dragon Ball villain, but he's also the best. Sure, little thought was put into him, but he proved himself to be a much bigger threat than Frieza ("I can gather energy a lot faster than my brother."). Also, the reason why the English dub of Cooler's Revenge is my favorite Dragon Ball film isn't just because of the villain: it's because of it's soundtrack and voice acting.