All three are good.
The Sprinter van doesn't have a frame. However, the cutaway does have a ladder frame.
The Sprinters are Mercedes. They work well, but when they break, you pay Mercedes prices for parts and service, especially if you lose a key, or a particulate filter gets clogged. You may not have a Sprinter dealership nearby, because not all Freightliner or M-B places bother to service Sprinters.
I would go with the E-450 as my chassis of choice. Granted the V-10 is a gas guzzler compared to the thrifty OM642 V6. However, the Ford V-10 is tried and true, and I've read about those engines taking insane amounts of neglect and abuse and still running. If I need parts, OEM replacements are present, non OEM stuff abounds, and there are tons of junkyards with those engines. If I need a new engine, $5000 gets me one from a crate, and I can get rebuilt/remans for cheaper.
