When I tow, its only a small 6x10 trailer for my toys (giant scale RC airplanes and helicopters). What I love most about our Class B (21') is the convenience of its smaller size and 'go anywhere' capabilities. Having owned larger RVs in the past (A&Cs), I wanted something smaller to travel in and the Class B fits the bill perfectly. I've not felt the need to tow or rent.
As others have posted, we also just hook up water or sewer as need to fill or dump. So its really convenient to just unplug electric, and a few minutes stowing gear inside and you're on the road. Even more convenient is that we have our home with us all day while out sightseeing for using the bathroom, meals, relaxing break from activities, etc. Avoid real tight parking lots, or low overhead parking garages. I personally can't see any advantage to towing a car with a Class B. Even if you rented often, it would take a long time to recoup the costs of a toad, setup, lower gas mileage, etc.