If I really had to bug out, I'm thinking my D8 dozer would be the way to go. Weld some steel plating on it and the thing is basically a tank. Off-road, on-road, trees, cars, trucks....very little stands in my way.
I don't know what kind of fuel mileage it gets, but I know it costs over $500 a tank to fill it.
With that in mind, I think anything is better than nothing. I'd rather have even a bycycle than be stuck walking anyday.