Oakley square wire with blue lenses for me. They have just the right tint, not too dark but sufficient for flying/driving/skiing etc. The blue lenses don't distort colour at all either, so no problems with the instruments (although that's for steam dials, I'm about to find out if they work ok with EFIS!).
The pair I have are years old, and despite the using my shirt to clean them (the oakley bag long since lost), by keeping them in a hard case they have not scratched at all. Highly recommended!