In Colorado, 32-34 is usually OK in the State parks, but limits the number of sites in Rocky Mt Nat'l Park. But of course, out here during the summer, if you don't make a reservation for the weekends sometime in January, you don't get in (but usually you can still get in during the week). I'd do a quick comparison on a website like "reserveamerica.com" where you can put in the RV length and see how many sites you lose when you go from 30 to 32 to 34 foot for the area that you want to stay. I think all of them will still have some sites for all of the lengths, but the number will go down with the size.
Colorado '15 Winnebago Forza 34T w/MKZ hybrid toad '20 Jeep Cherokee Trailhawk toad