I used to have a nice pair of flexon frames. (Lost in an accident that claimed 6 lives.)
I also have several pairs of heavier safety glass style frames.
I will never uses glass lenses again after having one shatter in an accident and leave a shard of razor sharp glass in my cheek.
Polycarbonates can be bought that are more resitant to scratching than glass is.
Plastic lenses also seem to be less likely to get burns and pits in them if you are working with a welder or grinder.

You should always have at least two pairs of clear glasses and if you need them one pair of prescription sunglasses (Polarized?) if you are going to be near water, snow, sand or other bright areas. They will prevent snow blindness.
In addition to my regular glasses I keep a pair of those incredibly ugly polarized "Fitover" glasses. The Fittovers are large enough to wear like goggles with my regular glasses under them.
For skiing and other winter activities a pair pf anber lenses are good because they increase the contours you can see in the snow. On onercast days even faily rough areas of snow and ice can look very flat because the shadows disapear.