My wife and I have owned two Mobil Scout now Sunnybrook trailers over a period of 10 years. We are National and State Park campers and rarely stay in a commercial park. Our first trailer was 26 feet with one slide and our second was 33 feet with two slides.
There were many places that we could not stay with our 33 foot trailer. However, we never were shut out of a park with our 26 foot rig. If your goal is to hit National parks then under 30 feet makes a difference in some of the parks that have not been updated. For example, last summer in Colorado we stayed in three National parks with no problem, but could not stay at the Great Sand Dunes NP and moved to a local State Park.
This year we bought our first Motor Home and specifically limited ourselves to 33 feet in length to try and make as many parks as possible. We have learned that you can put a longer MH in a spot than trailer, largely resulting from better shorter over-all length and a pretty good overhand behind the rear wheels.
If we were ever to go back to a smaller unit, we would make decissions on which model to buy based on Bed comfort, Bathroom size and access, and finally living room comfort. Time and time again those were the areas that we had the most complaints in with our first trailer and our pop-ups that preceded the hard sides.
Good luck and happy camping.
Dave and Anita
2015 Itasca Sunova 33C