Alloy is pretty strong if made well, its light and plyable enough to crumple
up in a large accident but difficult to repair. Steel is bloody heavy, very
strong and easy to repair but bloody heavy, did I mention that they are
heavy?. Poly, your better off useing couch cushions strapped to the front of
the car, they would fair better. They are okay(ish, for low speed low
impact)  new but when older they get brittle with the UV and smash to peices
if you even get close to armco.

Hey, its your dollars, and this is purely my opinion. Take it or leave it.

For a courier, you'd be better off bolting blocks of rubber to it. lowspeed
impacts, parking damage taken care of without the fuel penalty of a steel
bar.

-mark

Alloy can take a fair punt and protect the vehicle but sometime write itself
off in the process

I will sorta agree, and sorta disagree with the above replies. Assuming you
do not want to fit a winch:

Steel is the best but (1) too heavy and (2) rusts....yes even the
powdercoated ones.
Poly is great (no it does not get brittle, any half decent one uses UV
stabilised plastic)  Buuttt it is too flexy. They flex so much that they
come back and cause panel damage so are not much better than no roo bar.
Save your radiator so you can keep driving but the repair cost will be just
as bad as no bar at all.

Thus:  alloy is right in the middle!  Perfect for most of us.