They both have different sound transmission. One has a low frequency sound, the other is high frequency. They both work well, except the more expensive one transmitt the sound more clear, and works well with people who can't hear very well.
Back more than a quarter century when I faced this question, we referred to the cheap stethoscopes as "cardiac detectors". WelchAllyn was the brand most of us chose back then. Your choice may in part depend on your intended use.