What are the advantages/disadvantages of both, and which one would have the least fitment issues?

If you paint the PU and it bends, will the paint get a messed up?

 

i would go with PU.

slight bending would not crack the paint, bending it too much will

 

The ABS is cheaper, but it's a lot more fragile. Polyurethane is what your factory bumpers are made of, so that gives you a good idea of how durable it is. As far as fitment, you shouldn't have an issue with either material. Personally, I'd go PU; it doesn't take much to shatter an ABS lip (I know from experience).

Like sfazngiants said, a little bend won't crack the paint but don't try to fold it 180* or anything like that.

 

^^^ what they said

i chose to try abs at first to to save a bit, but after cracking and tossing two, i chose to pay like ten more dollars for pu that has bottomed out a lot, and if it wasn't stolen i'd still have it lol