I have quite a few pairs of sunglasses, Oakleys, Ray Bans etc and wear different pairs for different occasions, but I will only fly in my Ray Ban RB3187's.
Graduated mirror lenses, very light, double sprung arms (so they don't lose shape) and perfect light block.
The graduation is very slight but you can easily read the map, the GPS and instruments, whilst having a perfect light balance for spotting other traffic or making a late evening 24 landing.
They also look really good
bs