Get a pair that slightly curve in. This stops the sun bursting through the side.
EG:
RB3218 model
RB3331
RB3273
Don't get a slim pair as you will be squinting all the time.
Duty free in good airports have a good selection these days.
STN especially.
Don't get the drivers lenses. They are not dark enough in my opinion, but that is a personal opinion. Darker ones do, however, make the glass EFIS a tad harder to see, but it beats getting sore eyes from the sun.
Try and try a few if you have any friends with different shades. All our faces are different, and some may hurt you with heatsets on. Oakley is a prime example.