Glass is naturally better for optics and polarization than poly. And it's more durable in terms of scratch resistance. Less durable in terms of breakage/shatter, hence glass lenses are usually fully enclosed rather than having the bottom of the lens exposed like many poly lenses. And heavier, although the modern better glass lenses are usually pretty thin as to not be overly heavy.
Regarding polarization, poly varies a lot depending on how it's done, but at it's best, is probably still inferior to glass in that respect.
That said, these are sunglasses. With optics and polarization, there reaches a point when you are "good enough" and any differences beyond that are in the realm of scientific testing, and probably not noticable by your average human being. Perfect optics becomes much more important when magnification enters the discussion, in things like telescopes, cameras, binoculars, and rifle scopes.