Personally I think the butterfly stroke is the coolest. I love doing it more than freestyle. Whenever I do, I feel like I am swimming like a pro. Since some consider it to be the hardest stroke, I feel like I am being admired when people see me do it, and yet they can't. Among its positive effects on me is that it exercises my core more than any other stroke, which I really like and really motivates me to keep doing it and be better at it. Another thing is it strengthens my arm and my back muscles. I remember that when I had my muscle soreness, I just kept swimming, I did butterfly and somehow it eased the the terrible soreness that I was feeling.