If you want a self-contained Class C with the flexibility for occasional camping without hookups, you better take into account tank sizes between models on your short list.
Tank sizes is often not paid much attention to by buyers .... and they do vary a lot between manufacturers of models in the same range of sizes and lengths that you might be interested in.
Using our small 24 foot Classs C as on example, I would not want tank sizes any smaller than they are ... but after years of comparing competitors, our tank sizes are on the upper end of capacities for our RV's size. Our tanks are: 29 gallons of grey water, 39 gallons of black water, 44 gallons of fresh water (including a full water heater), and 18 gallons of propane. These are about the smallest tanks I would look for in any size Class C ... I wish our capacities were more and there's plenty of voids in behind walls and down along the frame where larger capacities could have been installed when built.