For the DW and me, it needs to be small enough to drive through small towns to five d quilt shops and gun shops. Ours is 25 ft and fits the two of us.
My recommendation is to rent the size TT you think you want and tow it around for a week or so. You will learn a lot very quickly before you part with your big money.
We are canoe and tent campers but for travel and sight seeing we bought a TT. We have towed over 20,000 miles in the last three years and never had an issue with a 25 ft length though a few of the older campgrounds were tight.
One thing I miss with the TT is the feeling of camping.
Twenty six foot 2010 Dutchmen Lite pulled with a 2011 EcoBoost F-150 4x4.
Just right for Grandpa, Grandma and the dog.