When we first started looking for our coach, I was REALLY into the Sprinter platform. That fuel economy looks wonderful. However, it wasn't too long before I realized it wasn't going to be a good fit for us. Here are the main reasons, IMO.
1. Significantly smaller than many other class C options. I'm 6'-5", and DW is 5'-11". Lower ceiling, small bathrooms and shorter beds were all nonstarters for us. Plus, neither of us has any interest at all in corner bed configurations. Trust me, no way I can crawl over her without disturbance!
2. Onboard genny is almost always LP, and the tank usually isn't very generous. An LP genny can burn a lot of gas relatively quickly. Diesel upgrades are available on most, but it's around a $6K upgrade!
3. $15-25K price premium over many comparable coaches on Ford chassis. Ouch.
4. Significantly more costly to maintain and repair. There just aren't a lot of Mercedes dealers around with the large facilities needed for such a vehicle. You may be hundreds of miles from one when a problem arises. Parts are significantly more expensive, as well. Conversely, there's a Ford truck dealership on every other corner across the country, and parts are cheap and plentiful.
5. Much lower cargo capacity. The GVW ratings on the 3500 Sprinter are just much lower than an E-450. When you get you, your spouse, full tanks of water and fuel and your normal "stuff" inside, many units are already overweight. In that state with our E-450 based, 27' coach, I still have over 1500 lbs left before reaching the red zone.
That said, you should get what works best for you. These points may not be important to you, and/or worth the better fuel economy. I'm just sharing the disadvantages I saw, and they were serious enough to put us off that style of coach.
Good hunting!