Agree with Bob that a 20ft is probably the most versatile. There won't be too much room in the front with a car in there, but with some cabinets, the space can be optimized. I pull a 28ft trailer, fully finished inside, with a Ford Expedition, 5.4L. It gets a whopping 6mpg hauling that one. A diesel truck is best for pulling an open trailer, but it's hard to justify the expense if only using the trailer a couple times a year.