I have been really busy the last few days, so I will weigh in on this.
Disclaimer: While my professional training makes me an "expert" in this area, I do sell sunglasses, both prescription and non-prescription in my practice.
Polarized: Just remember what a plain polarized lens does. It simply blocks light that is vibrating in that plane. Light from the sun or other light sources is not polarized. However, reflected light is plain polarized. Lenses that are polarized are oriented to block light that is polarized by reflecting off a horizontal service. So this generally works great for light that is reflected off water or snow. Polarized lenses are a laminate of two pieces of lens material with a plastic polarized film sandwiched in between. The lens material can be plastic or glass. Be careful, some LCD displays will not be seen while wearing polarized lenses as an LCD is polarized so the display will blank out depending on the orientation.
Eye protection: It is a good idea to protect your eyes from the sun just as you would your skin. UV radiation is the problem and has been correlated with earlier onset of cataracts and the development of macular degeneration. For this reason, it is a good idea to wear a hat and use sunglasses. For this purpose, almost any pair of sunglasses that you buy from a reputable source will be just fine. If they are labeled as being 100% UVA and UVB absorptive, they likely are here in the US. I would avoid the $3.00 pair at the gas station checkout, and careful of off shore internet sources, but other than that the industry is pretty good these days about accurate labeling. Another option, for those of you who use photochromic lenses (Transitions) they are UV absorptive as well so will provide perfectly good protection.
Color: Gray is the color that will have the least impact on color perception and is what I recommend to my patients. However, pick a color you like, it really doesn't matter. If a blue, amber, green or brown lens makes you think you see better, go for it. A lot of research has been done on the use of yellow lenses in the shooting sports and with pilots. It is clear that pilots for example as a group prefer yellow lenses and will swear that it reduces fatigue, increases visual acuity etc... However, when actually tested, yellow provides no more increased performance than a neutral density filter in visual acuity or contrast sensitivity.
Glass vs Plastic: Pick what you like it doesn't matter. I would never go back to using glass lenses myself. Plastic lenses are much lighter in weight and therefore more comfortable to wear for an extended period. Modern plastic lenses are optically just as good as glass lenses (provided they are made well). Modern scratch coatings are almost as hard as glass. Plastic lenses provide less risk of shattering on impact.
Prescription Sunglasses: One of the nicest things you can do for yourself. Once you do, you will never want to be without them.
Photochromic (Transitions): These are the lenses that get darker or lighter depending on the amount of light. I actually love these and use them on all the glasses that I wear outside the office. They are 100% UV absorptive, convenient as you don't have to carry a sun Rx around. They do have disadvantages. Since they are UV sensitive, they will not get very dark inside a car where the windshield will block UV. The same thing can happen in the boat depending on the type of wind screen you have. The second issue is that while they darken quickly, they don't lighten up quickly, so going from a bright deck to a dark engine room for example could be an issue at times.
Cost: In many respects, you get what you pay for. Nothing wrong with cheap sunglasses since as mentioned above, the cheap ones will still provide good sun protection (the primary reason for wearing them). However, it is difficult to manufacture non-prescription plastic lenses without distortion. Cheap sunglasses are cheap because the frames are poor quality and their is less QC involved in the lenses. So with cheap sunglasses, you can randomly find very good, and very poor lenses even on the same pair of sunglasses. Higher quality (and higher cost) sunglasses have better QC so you are less likely to come across optical aberrations in the lenses.
For this group, which is made up of primarily old farts with plenty of disposable income, there is no excuse to not get yourself some good quality prescription sunwear. Simply put, if you are 45 years old or older, you cannot see clearly both in distance and near. Many men in particular try to fool themselves into believing they can, but it is self delusion. By the time you are 50, you are seriously impaired in your ability to read a chart or display clearly. Time to invest in some multi-focal lenses to wear generally, and consider prescription sunglasses with both the near and distance prescription.
