Lefty- It all depends on the size of the fly that I'm throwing and what the conditions are. I use a 4/5 weight for smallmouths in creeks, but I also use up to a 9 weight for largemouths in heavy cover (no finesse there!).
If I could have only one rod to cover all of the conditions, it would probably be a 6 or 7 weight that can throw a variety of fly sizes and still have enough backbone to wrestle a hawg. Yeehaw!
Sorry, watching those BASS tournaments on the tube is starting to rub off on me.