As Sierra mentions - it depends on where and how I want to utilize the tool.
I have several 3, 5 and 7 weight rods ( TFO's mostly ). I like to fish close and smaller waters when possible. The upper Deschutes and Rogue are fav's.
I prefer to nymph and dry fly with the 3 weight mostly - the 5's are my all around guns and the 7's are used on bigger waters and slinging heavy tandem nymph set ups or salmon flies.
I don't go in for long rods - I can fish from my boat on the Rogue and position as needed - the smaller stream just don't warrant them.
Unfortunately, I have a bum shoulder and the 7's beat me up rather quickly, and they don't get a lot of use these days....