Get a 34 footer.
I have a 34 foot triple axle and if any trailer tows "like a stream of air", it's the triple axles. They pull just as easily as a 31 footer (my last one). Actually scratch that; they pull BETTER than ANY double axle trailer. The triple axles really pull nice.
If you can park, you can stuff a 34 footer just about anywhere. They are still VERY SMALL compared to the fifth wheels that you see most people pulling.
You get more room, stable pulling, and just more to love.
I'd like to add an 18 footer to my stable (my grandpa has a
1958 18' Traveler that I want to buy), but other than that, I have no use for anything in between.
You 25' guys, if you like 'em, my hat is off to you. But I think the long boy pulls just as well if not better, and you get a lot more room. And like the others said, none of these tubes will have the room of a white box, so you want all the length you can get.
My vote is for a 34 footer with a slide out.
Best of luck!