Without getting technical the best choice for sunglasses are Polarized lenses. They block glare reflecting off of objects.
Real life examples are as follows:
- Driving down the road and the sun reflecting off the back window of the car in front of you.
- Boating or fishing and the sun reflects off the water.
- Driving while its raining and the sun reflecting off the wet road.
The most popular polarized colors are grey, brown, and Drivewear Polarized Transitions.
Grey is the best for the brightest conditions. Also good for deep water fishing.
Brown is a good all around lens. Also good for flats fishing.
Drivewear is good for driving, rainy conditions (during the day), golf, cloudy or overcast days.