-- Last Updated: Jan-31-13 11:15 AM EST --
The perfect rail for durability would be a stainless steel and spherical. Everything else is on a durability continuum which is just one rail system characteristic. One piece aluminum extrusions do not capture the laminate nearly as integral synthetics. Aluminum rails also tend to flatten shear and create hog in canoes.
I have seen synthetic rail boats that have exited roof racks at road speed without damage to the rail system; end over end flips that have bent aluminum rails beyond utility or repair and shattered wood systems.
There is variation in synthetic rails. A local builder came up with a rain gutter system compatible with hand lamination; ingenious in concept it was built too lightly in it's first iteration. They got it right pretty quickly.
Savage and Crozier install synthetic rails after the hull is infused. Colden, Placid and Swift infuse their symthetic rail systems with the hull. The weight savings are pretty heroic, roughly 15% of total hull weight.
A useful analogy might be fishing nets. Cabela's lists aluminum framed nets from $60-$170, mostly $70+/-. WalMart must under cut that range. Nomad makes smaller trout oriented nets with infused frames; lighter and elegant, running $115-$230. We get to make our own choices.