I've always thrown the "turnover" or "rollover" drop, personally. It's just what I learned when I began pitching, so it seems to be the easiest and most effective, but it's not for everyone. When I started giving lessons and researched the different styles for different pitchers, I found the "peel" drop and tried it out as well. I wanted to be sure I could help any pitcher who already threw this style drop and also offer different options to my pitchers just learning. What I found out was they were both effective for different types of girls. To some, the turnover is just too awkward a move to pull off unnoticed. For those girls, I taught the peel.