I'll chime in because I have two kids that sell sunglasses for living. One works at Sunglass Hut, the other kid works at an Oakley store. Their parent company is the worlds largest retailer of glasses, both sun and prescription, and they own Ray Bans and Oakley among other brands. Because of this I've got some great gifts of expensive sunglasses over the years.

First, most any plastic lens will filter UV light, even clear lenses. Polarized lenses reduce glare. I always wear polarized lenses that filter UV.

From the starting point you're really looking at len "optics" (clarity and distortion). Quality lenses have great optics. Ray Bans, Oakleys, and Maui Jim's all have high quality lenses, and then there's also the quality of the frames. They all offer different styles and types of frames, and all of them are high quality, but some of them are better suited for hiking and rough use.

Of those three brands, Maui Jim's are my own personal favorite. They're incredibly lightweight, very comfortable, and quite durable. The frames are very flexible and not prone to breaking. Most Oakleys are OSHA approved safety glasses, and you can easily change out the lenses in some of their styles.

That said, Ray Bans, Oakleys, and Maui Jim's are all way over priced. I would never pay what my kids sell them for and you can get good optics and frames in much less expensive glasses.

Wal-Mart is the second largest retailer of sunglasses and most of what they sell is crap. To test them hold the lenses away from your face, look through them as you move them slightly up and down while focusing on something in the distance to see the distortion in the lenses. They're awful. That distortion can actually damage your vision if you wear them a lot. To test clarity in the store you really need to hold a good pair next to any other pair. That's about impossible to do in Wal-Mart unless you bring them yourself.

Oakley's and Ray Bans are now made in China. Maui Jim's are made in Italy and Japan. I think it's safe to say that about all the sunglasses in Wal-Mart are made in China.

You can buy good Chinese sunglasses for comparably very cheap at www.AliExpress.com. You have to wait a few weeks to receive them because they are shipped via a slow boat from China. The glasses you find there can be low quality crap, or they can be pretty darn good. Generally speaking, the more you pay the better they will be.

They sell knock-offs of both Ray Ban and Oakley there pretty cheap too. Be aware that they are knock-offs and you can't legally resell them in the U.S. You can buy no-name Wayfarer knock-offs for as little as $1 a pair there, but the lenses are crap. Earlier this year I bought a pair of Oakley knock-offs for about $15 and they were pretty good. Not as good as genuine Oakleys, but much better than most Wal-Mart crap. I bought a few other pair there too. One pair was a $6 pair of metal framed polarized Aviators. Those are a pretty weak design, even the Ray Bans will get easily bent, but the cheapos I bought weren't too bad. The optics were pretty good considering the price. For comparison, I also bought a box of a dozen "Wayfarers in Fashion Colors" for $1 a pair ($12 for the box). The frames on those were pretty good, but the lenses were crap. Almost exactly what you get at Wal-Mart for $15-$20.

For those who might care, the best sunglasses for fishing are polarized and have a light tan colored polarized lens. Most fishing glasses are polarized now and most have a dark grey lens. They both let you see "Under water", any polarized lens helps with that, but the lighter tan lenses let you see much further under water because they let more of the light get to your eyes. I've tested this throughly myself with many types of lenses in many colors and shades of darkness and had many friends test it too over many years while fishing.

And I'll +1 on getting a lanyard for your glasses. I don't like hanging them around my neck at all, but it's the only way I can keep from trashing or losing them.

I generally don't wear my sunglasses when I bushwhack anymore, they get snagged up on branches if you let them hang off a lanyard. I've broken them doing that, so now I bring a soft case (a soft drawstring bag made for them) and put them in my pack. If I were traveling like you intend to, I'd bring a hard case and I'd use it.