I run 46/17 because it seems to be the standard. I don't have too many hills, and I don't usually feel like I am spinning out ever. Seems to be a happy medium. That said I have heard that lower is better, I have an 18t cog lying around 46/18 would be a nice little drop if I wanted to try spinning. i also hav a 42t chainring I could plop on there.