I have never owned nor even test driven the Sprinter, so keep that in-mind when reading my reply.
We own a PC2350 built on a 2007 E350 Ford chassis. 2007 was the last year of the lesser E350, so it handles 1000 pounds less weight and assumed a less bumpy ride because of it. Mind you that our ride is still bumpy especially considering that our rig is lighter because it does not have a 400 pound slideout. As mentioned by ragoodsp, the closer you load your rig to the limit of the chassis, the smoother your ride will be.
If considering an E350, plan on spending a few thousand more on more capable stabilizer bars and such. But I suppose a Sprinter would also benefit from the same upgrades.
Regarding fuel economy, that is quite subjective pending what you carry aboard, what you tow if anything, driving habits, whether you use cruise control, the types of roads travelled, generator usage, and how fuel economy is being calculated. My trip average is closely documented (each fuel purchase) for most accurate data.
All trips were heading out west
Trip towing 2100 pound car over 5000 miles - 9.5 mpg
Trip towing 3600 pound car over 4000 miles - 9.2 mpg
Trip towing nothing over 5500 miles - 10.6 mpg
A couple tank fulls got over 13 mpg, I recall one rough slow 15mph switch back mountain tank full got 8 mpg, but my averages were from home near Chicago, back to home.
There are other considerations, E350 versus Sprinter, some previously mentioned.
This I copied from my standard reply on this subject matter on another forum.
Advantages Of The Sprinter With Diesel Engine
- Offers a 35% improvement in fuel economy over the Ford-V10, when both are loaded and driven identically.
- More ergonomic driver compartment with more leg room.
- Comfort continues with a car-like feel & quiet ride.
- A grander view out the windshield
- Made by Mercedes which people are attracted to.
Advantages Of The Ford E350 with V10 Engine
- Given identical motor homes both brand and model, the Ford is around $13,000 MSRP cheaper
- The Ford V10 engine has 50% more horse power and torque
- The Ford E350 chassis handles 1430 pounds more weight.
- The E350 is able to tow a heavier load.
- The E350 rear axle is significantly wider which translates to better stability.
- In most places traveled, gasoline costs less than diesel fuel
- The Sprinter diesel has limited mechanical service shops around North America
- The Sprinter diesel is typically outfitted with a propane generator. Propane is a critical fuel for RV operations, and generally needs to be rationed when dry camping.
- This Next Point Is Debatable But Still Worth Noting....The V6 Sprinter diesel engine is not allowed to idle for extended periods. This limitation is detrimental when you need a/c but there are generator restrictions or you are dangerously low on propane, or you have a mechanical failure with the generator or roof a/c. The Ford V10 can safely idle for hours on end, heating, cooling, and battery charging, all valuable if you have a baby, pets, or health/respiratory issues.