Just depends on the rod location etc.

Smallest I had was the OO weight, largest is a 12wt Single Hand or 14ft 9wt Spey.

Western Rivers I am normally nymphing with a 9'6" Sage One, Dries is a 9ft 5wt Sage XP, Smaller Dries 9ft 4wt, Streamers 9' 7wt Helios or 9'6" Sage Method, Nymphing for Chrome is a Sage 99 9'9" 8wt.

All around I like a 9' 6wt. Its a little big for small rivers but if you were to get one I would do that. Its a good rod for the MO, Clark Fork etc. If you want a dry rod got 9ft 5wt. I just think a 5wt gets it done good enough nymphing.