Well, as a longer term update to mine:
Glasses: MJ Twin Falls. HT lenses in the MauiPure material. Comparing them often here to my Costa Fathoms in green mirror 580G (glass).
This is part of their "Pure Air" series, so they are incredibly light. They are much lighter than the costa's. That said, weight doesn't bother me much. The MJ's are also flimsy, and yes, I broke the frames already (MJ repaired them for $10 plus shipping). Other MJ frames seem much sturdier.
As for the tint on the MJ's. Not sure they're light enough to take me really into spinner fall time of the day. But they are PERFECT for cloudy weather, and brookie fishing under a thick canopy, both situations where the Costa's have proven to be too dark. Good driving glasses as well. They are suitable for bright sun as well but a bit on the light side for that, still, it's nice that they're suitable enough for any situation where you could wear sunglasses. For this reason they are used more often than the Costa's. But the darker Costa's are far better in bright light situations, and offer better contrast and seemingly clearer colors.
Polarization: Not quite as good as the Costa's, but still very, very good and far above the cheapies I have. I think this is more a difference between glass (unstressed polarizer) and plastic (stressed polarizer resulting from injection molding) than it is a difference between the brands, which are both known for very good polarization.
Clarity: MauiPure is better than poly. But noticeably not as good as glass (again, this is their "MauiPure" material, unlike tctrout who has their glass lens).
Other: The coating on the lenses seems almost oily. Takes a very noticeable fingerprint like nobody's business, and when you try to clean them, it seems to smear instead of clean. Again, their glass would solve this "problem".
Overall: I like my Costa's better, but wear my MJ's more as they're better suited for a wider variety of conditions.
In the end, I don't think it's a reflection of the brands (both very good), but rather that glass > plastic. Both brands carry both glass and plastic.