One of the primary reasons for a Class C, B or A over a 5th wheel is the ability to climb into the driver's seat and drive away from trouble without ever having to go outside or hitch up. Class C rigs drive a bit more like a car than either A or B, which you might also find helpful. In addition, there are Cs that are smaller than As and Bs.
I too would suggest renting a C from somebody like CruiseAmerica for a week so you get some experience before you put real money into buying.
I also agree that your needs will differ depending on travel plans, your job(s), pets, and how much "stuff" you want to have with you.
There are single people who find something as short as 17 or 18 feet perfectly acceptable, and others who feel pinched in a 35 footer.