My riding glasses MUST be Polarized. Glare reduction is paramount.
Next is color - I prefer an orange- to brown tint over gray because it seems to heighten colors/contrast rather than just darkening everything.
Spring temples are a plus so they aren't easily broken.
A more contoured-to-the-face shape cuts down on distracting side-lighting, but they also cannot fit so close that they steam/fog up due to exertion.
Scratch resistance is nice, too
Brand name? Not important.
Yeah, most of my sunglasses - even my DRIVING sunglasses - are sourced from discount or drug stores, but generally the 'better' lines, and still less than $30/pr Would I spend $150 on a pair of Oakley? No Frigging way!