The strength of a frame will come more from the way in which it is built than the starting material: the frame's structure will dictate its ridgidity/strength.
Chaka Ping wrote:
Carbon frames are typically more comfortable to ride than aluminum ones.
Though this doesn't apply so much on full-sus bikes.
Did you already rule out steel? It does offer a very good compromise between strength, weight, comfort and ride quality for hardtail frames.