I will also side on the "bigger is better" especially since you mentioned bringing grandma along sometimes and some pretty long trips, but you also have the experience from your TT and 5er to think about spac/size/layout and how your family camps and travels.
One thing that is fresh in my head is the jack-knife sofa. A lot of folks don't like them for comfort, though we don't think ours is too bad. My DS is 10 and he has slept on it a few times, as have his friends. I've slept on it once. No complaints (though I'll admit that it isn't as comfy as my memory foam in the back bedroom!) But the thing is that it can open and close so easily and the slide doesn't need to be out to allow someone to sleep on it. My parents have a class A with a similar floorplan to our C, but their sofa is a pull out. Probably a tad more comfortable (though I just polled DS and he says they're about the same)...however they can't pull out the sleeper if their slide is in. Just something to consider and make sure of as you shop. I'm sure the pullouts aren't all like that, just something to check on.
