Ray Ban are my choice. Unfortunately they have a light metal frame, so you'll need to keep them in a glasses case when they're not in use. And why are they better than others? Well one of the over-riding reasons was the same as Pushback's " you can see the instrument panel as well as outside. There are lots of sunnies that are great to wear looking outside, but when you look in at the instruments you can't see a bloodey thing.
A little more expensive, but an investment in your eyesight - something you need to protect, if you're going to rely on aviation for your life's income. Also, a doctor advised me early in my career that pilots are more likely to develop trigians ("spelling police"?) because of our increased exposure to UV rays, and to always wear sunnies when flying.
But perhaps the MOST important reason - sunglasses stop you squinting in glary conditions, and delay the onset of "crow's feet" around your eyes, and we all know the top priority is to stay "lookin' good".