I'm totally into non-profit schemes but from the math I did it seemed that CityCarShare came out more expensive than ZipCar if you want to take the car out of the city because they charge you $0.35c/mile in addition to the hourly rental.

(ZipCar don't charge per mile just per hour).

I also have appreciated being able to use my ZipCar membership in other cities in America and Europe, esp in emergences/unexpectedly.

I wouldn't say that being a nonprofit makes them any better from a customer service point of view. When I closed an account with them, they continued to charge my card and didn't refund my deposit until almost 2 months later.