When Ray-Ban stopped making Ambermatics (photochromatic from dark yellow - amber
to brown [warm] or gray [cold]) I had to chose another brand. Tried alternative Ray-Bans, Bolle, Oakley then settled on Serengeti Nantuckets.
While they're great for being out or looking out on a sunny day, they're no good when flitting through the shadows or looking back inside at a shaded dashboard (esp. EFIS) since they are intrinsicly dark lenses. My Ambermatics cut glare (no squinting), improved contrast (smoke/haze) yet allowed easy reading of instruments (including all EFIS colours) and quickly adjusted to shadows or IMC.
Someone mentioned Aviator style not wrapping around or fitting in a helmet - well, I can't abide glasses that you can see around the corners of or let sunshine in around the top or bottom edges and I've never noticed this happening with my 59mm Ray-Ban Aviators. Also appropriately sized Aviators do fit easily in a motorcycle helmet and Top Gun suggests the same inside USAF helmets
Seeing people wearing sunnies that let more sunlight pour in from above and either side, than through the front, puzzles me but I guess they look good in the mirror. Unfortunately for me Ray-Ban decided to trim their expensive professional product lines in favour of the more fashionable models (cheap to make - expensive to buy), so expensive-to-make Ambermatic and the related Chromax lenses were dropped.
Back to the frames - peripheral vision is important and many plastic frames intrude. That's another gripe I have with my Serengetis - take them off or put wire frames (Aviators) on and the world goes wide-screen. Other posters have mentioned the pain of a headset squashing the arms into their head. Wire frames are less likely to be felt at all.
BTW - the bendy hooked ear bit is called a cable arm in Ray-Ban-speak
These keep your sunnies on no matter which way up a P-51 driver might find him or herself.
Another thing about them - cable arms need two hands to put on. Most military (square) style glasses (Ray-Ban and Randolf) also have straight flat arms making them a one handed job to put on even with a headset in the way - and being wire and with a flat 'paddle', they should be relatively comfortable under a headset.
Further, wire frames are usually more compact when folded and can slip in a shirt pocket, while your typical full-wrap Oakley Eyejackets, Killer Loops and 'Alien' styles need a semi-circular case and cargo pants even when folded.
We're all going to prefer something others can't abide, but if it wasn't for fashion, pilots in particular might have a few more cheaper choices.