i can tell you from personal experience that urethane is definately the way to go, hands down, without a doubt, and any more cliches you can think of...
i personally kind of "jumped" my civic hatch, this was completely accidental...
it was a rise and dip in a back road that wasn't labeled or signed at all...
so long story short, the car did a nose dive and the only damamge to my urethane front was slight scrapage, but if it was fiberglass it would have been in pieces on the road...
another example, me and my friend picked up a del sol that got steam rolled by a F350 pickup... it had a wings west urethane front bumper...
as we were putting it back together we took the front kit off and set it to the side, we figured we would have to get a new one anyway... but we walked into the garage the next day and there it was sitting perfectly back in form...
and i'm telling you the thing was completely creamed... it was just that all the bent metal was holding it in its contorted shape... but if you let it just sit it will come back to shape... i wish i had pics, but trust me, urethane is well worth the money...