Carbon fiber is strong is one direction, or more, depending on how its laid up, but it isnt uniform like aluminum, so depending on how the frame is hit, it can either withstand huge amounts of force (when its hit the right way), or it can break without too much effort (when its hit the wrong way).

carbon is also easier to repair, i have seen DIY fixes on carbon frames that worked quite well, just some sheets of carbon and epoxy.