I would say brasso, it depends a little on the depth, for deeper scratches brasso will tend to round over the edges so they are less noticeable, but they are still there.
Word of warning, superglue, and standard window repair fluids don't exactly polish if your trying to fill a deep scratch, and most of the plastic ones have a strong enough solvent to make the plastic cloudy.
And final note, if its a UV sensitive plastic, that was coated rather than being in the mix, (you will see a coating being broken if you polish them), then you either need to re coat it in a UV lacquer or be prepared to keep it out of the sun.