The class B's on the Sprinter chassis get good mileage but repairs can be expensive. A class C on the Ford E-450 gas chassis get lower gas mpg' s but are cheaper to repair with many more places to get service throughout the country. I like buying new but there are lots of class C's that are bought by first timers an soon replaced by larger rigs. If you want the ultimate class C look for a nice used 31' Lazy Daze class C.
I would stay in the USA or Canada and not venture south of our boarders.