I would think a pusher would have better traction for forward motion since the engine is behind the drive wheels which could possibly mean there's more weight on them. That's only half of the equation, though. In the snow it's most important to be able to steer and brake. A good bit of weight over the steer wheels improves steering (up to a point. You don't want the back wheels to slip out); equal weight distribution improves braking, I would think..
So to answer your question: I have no idea!