While darker lenses look like they provide better protection, ultraviolet shielding has nothing to do with the color of the lenses.
But because they’re so cheap, you can probably buy an entire drawer full of sunglasses for the price you can pay for expensive brands.
Clean them with a soft, lint-free Sunglasses Outlet cloth. In a word, choose sunglasses that suit your style. If you want to extend their life, you should take care of them.