I would recommend the plastic tube intakes. Metal is a better conductor of heat than plastic. When you put your hand on the hot metal intake, the inside is just as hot as the outside.
Look in you cupboards at your frying pans. They all have a plastic/rubber moulding over the metal handle.
Also, most of your cooking utensils are made of plastic: spoons, spatulas, etc.
Just my $.02.
2012 Grabber Blue, V6, Manual w/ 2.73, 91H BAMA tune, Airaid CAI, Magnaflow Cat-Back Competition Series Exhaust, J&M LCAs, Hood Spears, Misc. Plasti Dip Accents