I have always used polarized lenses and LOVE them! I fly steam gauges and haven't ever had any problems. However, I will probably buy a pair of non-polarized sunglasses before I get my seaplane rating.
As far as brand, I don't have any brand loyalty whatsoever and will buy whatever works for me. What works for me may or may not work for you, as I wear prescription sunglasses.
Go to an optician, try some frames on and see what you like. I would spend the money and get a GOOD, COMFORTABLE pair of glasses though. Don't go cheap, these are your eyes we are talking about, not to mention the headaches (literally and figuratively), misery, and regret that will follow if you go cheap.
My recommendation is that you stay away from department stores and go to an optician. You can find some really nice, high-quality, non-prescription sunglasses at most optician shops. Browse the frames, lenses, and coating options and discuss your needs with the optician. All of the prescription sunglass frames can usually be fitted with non-prescription lenses, also most (if not all) regular eyeglass frames can also be fitted with sunglass lenses.
Know EXACTLY what you are getting, and know that you will be happy with it BEFORE you buy them. By going to a good optician, you can get more options and a custom pair of sunglasses that are tailored to specifically fit your needs and comfort, not just a run of the mill assembly line pair of glasses. Most opticians will also provide a warranty and assistance with repairs, adjustments, etc if you ever need it.
Also, if your sunglasses don't come with a HARD case, buy one. You will never regret that investment, trust me on that.