I think that a good pair of polarized glasses are among the top four most important pieces of gear(a little more important than a good rod, a little less important than good flys and a good line). So much of our success, pleasure and safety depends on seeing well. So, get the best you can afford. Get two or three pairs if you are flush.
Some thoughts:good glass lenses are better optically than good poly.
Glass lenses are more scrath resistant(they are more likey to scratch if they are plastic than glass ones are likely to break). Plastic might be safer, but I doubt it.
Plastic are lighter,cheaper and more comfortable.
Stay away from green and grey lenses. Copper,amber, brown, and yellow(for low light)provide better contrast.
Don't get really dark lenses unless you are welding. Fish are always lurking in the shadows, and in over cast and dawn/dusk conditions,we need all the help we can get. Get a cheap pair for scoping out chicks or dudes or whatever. They're hard to miss.
Make sure they fit well and don't allow a lot of light to relect on the inside of the lense.If you see relections, pass on those John Lennon specials. Think Bono. If they fit too tight, however, they will fog up easily.
I like the "Chums" and "Abel" retention straps(sounds like a painful treatment for incontanence). Your head will come off befor you lose them.
Good brands for fishing specs are Maui Jim, Costa Del Mar, and especially Action Optics(cheap frames, but good lense colors). I have heard that Oceam Waves are good too. Action Optics make the best prescripion glasses.
Get a tacky pair that you would be embarrassed to wear(big blocky frames with side glass). Think Elvis in a bass boat. That way you will only wear them fishing, and will be less likely to loose them.
This should be in the "Gear Section". I gota keep the numbers up.
One cast can change your day...maybe your life.