The Bolle Sidewinder
style are my preferred. I have an almost-clear version with a slight blue/purple reflecto tinge to them. They are fine in all but the brightest sunlight right down to streetlights at night. I cannot believe they only cost $15. (On special - they're now $20).
The darker ones I got were, well, crap. The Bolle Mamba
don't have a separate lens and frame. The ones I got were quite dark - but they 'bled' light through the frame all over the place - which I find distracting. They also had that nasty combination of not actually cutting glare and the added bonus of being too dark so that you couldn't see what was on the road in shadows. I found them quite dangerous, in fact.
I've since got a pair of the Sidewinders (above) with a darker lens. Darker lens = slightly more exp but less than $30. Still, very happy with them.