I think that you should buy the cheapest available that block UV and do not distort your vision. I've been told that your eyes are actually better-off (if you wear the sunglasses outdoors, and not inside an automobile, for example) by not wearing sunglasses altogether if you just buy el-cheapo plastic. (Auto windshields block UV).
Bausch & Lomb (Ray-Bans) are for optics-nerds.
Personally, I like my lenses to block UV and "polarize." The tint/shading is irrelevant to me.