I'll say ATV over 4WD. I had owned two 4WD and yeah..it's a great carving deck for iced, cruds, bumps, and of course groomed condition like here in east coast. As named, it carves like 4WD on the off-road.
But for Powder, you can find better floating decks easily, like ATV. ATV is wider version of 4WD, as Prior stated. But it feels much lighter and float much better than 4WD. I would choose ATV over 4WD for your area, Sapporo & Vancouver.