Welcome!
Bigger will get ou more room and options such as washer dryer pantry etc. Just remember that bigger 5th wheels require bigger trucks to tow them with. Make sure you have a truck capable of safely handling the 5th wheel. With my first 5th wheel I tried towing it with a 1500 chevy and discovered after one trip that my truck was really not that good at towing our new 5th wheel. The dealer told me that the unit was a 1/2 ton towable unit but it was a nightmare to tow.
State parks are known to have smaller sites. I think at 33 foot or less you should not have to much trouble but it wouldn't hurt to go on your favorite parks website to check and see first.
Good luck and enjoy!
Dave