If you're proportioned like me (6'1" 150ish lbs), the narrower one will work better, otherwise for most people the 6 3/4 seems the popular choice. I've ridden my friends 6 3/4 saddle and I get lots of contact and chafing in certain areas. He, on the otherhand, gave me the saddle I have on my roadbike currently because it was far too narrow for him. It really comes down to sitbone width, and for uber lanky guys like myself narrower = better.