My optometrist tells me that polarised glasses can hide highlights like reflections off aircraft wings.. so could make them harder to spot... she isn't a pilot though :)
I have prescription sunnies just for flying, they are not polarised and are bifocal, making reading maps and instruments easy, while also giving great long distance vision for searching the sky / scenery.
I am not a fan of progressive lenses and they feel like you have "tunnel" vision an can't so easily scan by moving your eyes.