From my perspective, it's less about the overall length of the trailer and more about the floor plan that fits how you anticipate using the trailer. Will you be weekends only? Weekends with a week to 10 day trip now & then. Extended trips of 3 weeks or more? Answer that question first - envision how you plan to use the unit. The suggestion that you rent one you think may be "the one" for you is an excellent idea.
After we decided on the floorpan, then we went with the trailer that was the shortest and lightest unit that would get the job done. We've been perfectly happy with the results for 16 years. At 28' with no slides and the need for only 30 amp service, there are very few campsites that we cannot use, and we don't provide entertainment for campground rubber-neckers who like to watch somebody try to park a gargantuan rig. JMHO