Length vs Width , Which do you prefer?

OK, so I'm about to pull the trigger on a new CT that I will be converting to a Toy Hauler / camper. My build plan would be to incorporate a small kitchen, shower, toilet, sitting area, and 2 twin murphy style beds. Planning on using this to go cross country and looking for the best size that will allow me to boondock, get in and out of parking lots/gas stations easily, and basically be light on my feet while traveling. I'm torn between going with an 8.5x16 or a 7x18. I would go smaller but I think these 2 sizes allow me to put everything I want into it plus make the wife comfortable. Opinions?