Depends on what you want them for. If you're flats fishing in the tropics, you will need a very dark lens. For trout fishing, my current favorite fishing sunglasses are by Kaenon Polarized.
The model is the "Kore" with C-50 Lens.
I bought these sunglasses for only one reason. They allow the most light transmission for any polarized sunglasses that I know of. Kaenon sunglasses are available with a number of different lenses, and the C-50 lens is copper colored (hence the "C") and allows 50% visible light transmission. Typical polarized fishing sunglasses allow about half that amount of light. For example, my Smith/Action Optics sunglasses with a polarized, photochromatic "all conditions" lens allows a maximum of 28% light transmission.
So why am I looking for sunglasses that don't block the sun? It's because when I fish, I need the polarization feature to cut the glare and allow me to see into the water, but I don't often need a really dark lens. I don't fish on white sandy beaches or other super bright places. I typically am fishing on mountain lakes or streams. It's sometimes shaded, sometimes cloudy, and I sometimes fish until the evening.
A lens that blocks 50% of visible light is fine for these conditions. In fact, I've found that my depth perception and general vision tends to be better if my sunglass lenses aren't too dark. Like a camera lens, your eye focuses more easily if the pupil is not too dilated. With darker sunglasses, I would often remove my sunglasses when threading hooks and tying on flies. I could just see more clearly and focus better without them. With the Kaenon's bright lens, this is no longer an issue.
The quality of these lenses is superb. They are made from a new plastic material that Kaenon calls SR-91. It's lightweight, strong, and has excellent optical clarity. I am pretty sure that the lenses are made from the same material that the new Julbo mountaineering lenses are made from, (that Julbo calls "NXT".) In the light, C-50 tint, the lenses just seem to sharpen everything up, and they are just dark enough to be soothing to the eyes. Even when the sun is shining brightly, I don't experience any eye fatigue from fishing all day.
The frames are very comfortable and reasonably light weight. I can wear them all day long without noticing that I have them on. The sunglasses come in three different lens sizes. I just ordered a medium, and it seems to fit me well. If you've got a small or large face, you have the option of buying the Kore with small or large lenses. They came with a nice case and a soft bag. Overall, I am very pleased with the Kore sunglasses.
I bought them thinking that I would use them only in low light situations such as dawn and dusk. However, they work so well that they have become my primary fishing sunglasses even in bright light. About the only thing I don't like about them is the price. At around $200, they are pushing the edge of what I'm willing to pay for a pair of sunglasses, no matter how great they are.
And, just in case you're wondering, I fish a lot. (2-3 days a week during the summer and fall.)
I've used sunglasses by Maui Jim, Action Optics, Julbo, Oakley, and others.