I would suggest that folks always go for the smallest/lightest trailer possible because bigger only invites more issues. Having done your research and found two models, pick the lighter one. Three people, even if all are adults, will fit in either trailer just fine.
I have done the coast to coast and back thing and become a fan of the 2-2-2 rule: drive only 200 miles a day, so you can arrive by 2pm, and stay 2 days. Well, ok, we go 250-300 miles max, and we don't usually stay 2 days, but that's only because of limited vacation time.
Since you are so new to all of this, I would highly recommend taking a rented trailer on a few weekend trips close to home to get your feet wet first. You will learn far more doing that than we can possibly tell you here.
