I have owned the Chevy Rt, which was a great van, and driven the Ford Transit. if I didn't need the larger tow capacity, which is a non issue for most Class Ber's, I would get the Transit V6.
It's more comfortable to drive (jmo), quieter, and gets better MPG., also does better in the mountains because of the Eco Boost engine. There's no fiberglass roof to maintain, or leaks to worry about.
As for the Sprinter, I don't like the price, or the higher service fees, and lack of repair centers concern me. Parts are often not in stock, and can sometimes take weeks to get. But mainly I don't want a diesel.
I also don't like the Promaster, for reasons I will keep to myself so I don't offend any owners, and take this thread off topic.
