I use plastic PET carboys ("Better Bottle" brand) for fermentation, mainly because they're cheaper, lighter, and safer. I use only chemicals to clean them (no brushes), so I'm not too worried about scratching.
However, I'm getting ready for my first lager and wonder if I should get a glass carboy, since the beer will be sitting in it for much longer and I don't want too much oxygen getting in. I've heard that PET bottles have pretty low oxygen permeability (compared to a plastic bucket, say), but it's probably higher than glass.
So is it worth it to get a glass carboy? Or is my airlock / stopper going to let in way more oxygen comparatively, and it doesn't really matter what the carboy is made of?