Depends on if you are planning on painting.

Hardie (cement board) if you're painting, redwood or cedar if not.

Also, use ring shank stainless fasteners. The rings will prevent "walking out". I've seen siding nails walk out 2".

If it were me I'd never paint again. I believe a piece of wood will last longer not painted if it is allowed to breath. Placing the grain vertically helps longevity as moisture drains better.