The responses will be based on where people camp and what part of the country they live. I have been to remote areas designed for tents and small campers where 20' was the maximum length. In a nut shell the smaller the trailer the more areas you will fit. I would advise you to look at the campgrounds that you would likely go to and see what their length limitations are. Lenth may/may not be a issue at all.
I bought a large 5th wheel and hardly use it. I ended up purchasing a smaller TT to go to more remote areas. The TT gets way more use then the 5th wheel. On the positive the 5er still looks like a new unit.
For where I like to camp 20' to 24' seems to be the ideal length. I have been limited by height and length at very few campgrounds.
