Graphite is probably the most cost effective and it will absorb the impact and return to shape unlike your aluminum. I stay away from aluminum parts except for shock towers and other heavy duty machined parts for just the reason you mention. Carbon fiber will stand the most abuse but it's pretty pricey and there's a danger of tearing out the mount holes. I have gone back to composite CVD bones too - get an impact just wrong and bend the aluminum ones and they'll shake the car like mad (which doesn't help handling ;-). The plastic (composite or graphite) arms will also absorb part of the impact energy by bending before they pass the rest on to the chassis so they will help and you'll break a less expensive and easier to replace part if you do bust something.

Those aluminum parts look great but any that are cast or made from a plate instead of machined are likely to bend so they can be a headache. The stuff that can be easily cast is a far inferior grade of aluminum to the stuff they use for machining. [link=http://www.aircraftspruce.com/catalog/mepages/aluminfo.php]Here[/link] is a good reference for aluminum grades if you are deciding if the parts you are looking at will stand up to the abuse,