I don't know. I'd say Friction is more precise because you can put the chain exactly where you want it rather than only where those little clicks let you. On the other hand, SIS is easier for someone who is less experienced. You don't have to think about it; if the pedaling gets to be difficult, you just push the lever until the next click, and suddenly the pedaling is easier again. With experience, friction gets to be as easy and more functional, but it's one more thing to think about when starting out. I'd probably compare friction vs indexed to manual vs automatic transmissions in cars but less of a difference. Friction isn't as hard as a stick shift and indexed isn't as easy as an automatic, but it's kind of along those lines.