In ABC sport engines ,you buy OS (and Saito 4 strokes) when you don't want to have to worry about them working right. I'd put Fox into that category too, although they aren't as popular as they once were. You buy Thunder Tiger because they are cheaper and almost as trouble free (that multi piece needle valve design can leak sometimes but is easy to fix). You buy ASP, Magnum, and a few other designs because they are cheaper still and usually work. Fandom of the various brands comes from what your values are. If you like cheap things and don't mind having to put a lot of time into one occasionally to get it to work, then you'll talk up the cheaper engines. If you're a fan of horsepower and reliability and don't care much about the price, then you'll talk up OS and a couple of others.