Go with the E450 chassis if you care about overall size of your Class C.
A lot of folks don't care about that, as they primarily camp only in established campgrounds with enough room for RVs. However, that kindof goes against four wheel drive ... a 4X4 is "in it's glory" when offroad not anywhere near established campgrounds ... but out in the middle of nowhere is where the compactness of an RV is high priority.
IMHO, if you go for a Class C on a truck chassis keep the coach area as short/small as possible to help compensate for the long truck hood sticking out in front and it's overall long wheelbase. Just as a reminder, offroad use is enhanced with a short overall vehicle wheelbase so as to reduce hangups on bumpy ground.