I have the biggest problem with scratching my sunglasses. I have a nice pair of Versace sunglasses that are in the back of my closet and are never touched because I scratched a bit of the lense. Marc by Marc Jacobs sunglasses are a good alternative to expensive designer sunglasses. These sunglasses do not cost as much (they usually run around 100), they have a warranty of a year, AND they are fashionable.
My sunglasses are the oversized type. They are my evening sunglasses (where its a bit sunny but not so sunny that I would have to squint my eyes). I love them and wear them everywhere. Recently I lost them for a few weeks and found them underneath a couch cushion. I was horrified because I thought that I ruined them. I took the sunglasses out and the lenses weren't scratched, but the plastic was a bit bent! My beloved sunglasses were crooked. But I am thankful that I did not pay so much for them and they were easily bent back when I took the pair to Solstice!