[DJCarbine]

I would say that plastic is more prone to cracking further down the line after several years of heat cycling. I would also feel better cranking down on a t-bolt clamp on a coupler attached to an aluminum pipe, versus the same situation but on plastic pipe.

OEM applications come with plastic pipes, but there is an aftermarket for aluminum replacements. People like aluminum, I personally prefer it over plastic. Find a 90's BMW with plastic parts (Thermostat housing, water pump impeller, radiator endtanks etc.) and you will notice that most people replace with aluminum due to failures from age (premature failures IMO)