Thought i'd throw my 2cents in. Just recently bought a pair of Serengettis. The lenses are Photochromatic (Adjust to lighting conditions), Drivers Gradient (Which is their own brown colour lenses) and have their S Flex arms as well.
These are the best sunglasses I have ever worn and have everyone i've leant them to so far has agreed, they've even earned the nickname "The Rose Tinted Glasses", the world literally becomes a brighter, sharper, clearer place when worn. The Photochromatic lenses adjust without you even noticing allowing you to walk from a dark hangar straight out into direct sunlight with no problems at all. They wrap around nicely stopping sunlight coming in from the sides and above and below and with the S Bend arms they are incredibly comfy.
Admittedly they are expensive, but if you go to the right places and mention your a pilot and certainly in Australia you can mention you have Private Health Care they'll give a hefty discount, I got mine with 20% off from Sunglass Hut by mentioning both those facts allowing me to purchase them for only $336AUD.
If you don't mind the price tag, I highly recommend these, but be sure to get the non-polarised ones, which are actually a bit cheaper as well.
AND NO, I don't work for Serengetti or any other related company before anyone asks
