Depends on what you want & how you'll use it. I know vendor Larry Stock of PPC-Carson City has both metal and fiberglas front air dams & spoilers in stock (he makes them from scratch, but not all possible variations). Running a low mounted racing front dam on the street is foolish IMHO because you WILL eventually smack something with it. A metal air dam will bend if hit while a fiberglas one will crack or shatter. Both will crack paint if only hit lightly but can be fixed although in very different ways.
I had a 3-piece 'glas spoiler on a commuter sporty-car that I autocrossed every weekend, and after numerous hits and repairs, I finally changed the center section to .060" sheet aluminum, which I could straighten with pliers on the car, then rattle-can-paint to look halfway OK. I now have a mild fiberglas Revson on our Pantera; not low mounted at all, but it still got hit (and repaired) twice in 10 years.
Probably the best idea is a not-too-low mounted spoiler with a stiff urethane strip hanging down underneath near the lower radiator channel, to increase its effectiveness. Urethane will bend if it hits something solid, then spring back. This will be much like '80s/'90s Z-28/Firebird under-nose spoilers. You must select urethane thats stiff enough to not fold up under strong air blasts such as you'll get at high speeds. A folded up spoiler on the highway doesn't work and simply looks silly. Too bad no one makes a molded urethane Pantera air dam.