I want to bring up a point that I didn't see posted yet. With a Class C unit and some gas powered Class A rigs, it's not the length or storage area that are most important. IMHO, it is the OCCC (Occupant and Cargo Carrying Capacity) that is (maximum weight of all people and stuff you can carry in a given RV).
A new Ford E450 chassis has a gross maximum weight of 14500 pounds. All E450s are delivered to MH factories the same. Where they vary, is the weight of the house "box" and options the various manufacturers put on the chassis.
You need to find the sticker that lists the OCCC in each rig you are considering (do not depend on the sales rep to provide accurate info.) and determine if the OCCC will meet your needs. Some factors that reduce your OCCC are length of the RV (longer generally reduces OCCC), slideouts, automatic leveling systems, and other options.
Now this is important. We have been inside new rigs at the shows that would have been overweight with just our 4 family members on board, no stuff (food, water, clothes). This includes Class A gassers as well as Class C rigs. Yep, they had eye-candy though. No, the sales rep didn't know the OCCC.
So, when considering your unit try to determine how you will use it most of the time. Will you need to carry food or clothes for long cross country trips? Will there be family friends along for the trip? Mostly be used for weekend getaways to the beach? This will guide you to your weight requirements. Once you know this, you can find a floor plan that meets your needs. Remember, it is not how much storage you have, but how much weight you can safely carry.
Good luck on your search.