stainless steel vs aluminized steel, mandrel bent vs regular bent

I am considering what muffs to put on my 72 barracuda (318).....

But one area I think I need to determine first is stainless steel versus aluminzed and mandrel bent versus standard bend....

The local muffler shop I am considering using for the exhaust does standard bent, aluminzed steel......now they seem like nice folks and seem to be very "into" doing older cars like ours....they will craft an x pipe for me, install the muffs of mu choice and all for a good price....

But I know stainless will last longer and that mandrel is "better" as far as flow.....

SO, what do you guys run and why?