Frame: White
Lens: Black Iridium
These were the only M-Frames I've ever owned. I picked them up for $40, and never regretted it. They were purpose-built and very functional. My only complaint was that they didn't fold, and it isn't much of a complaint, since they weren't designed to.
Frame: Joker
Lens: Gold Iridium
I honestly bought these solely for the Joker frames which are unlike anything that Oakley currently makes. They are a tight fit like all of the Oakley sport performance frames but their legendary reputation is well deserved.
Frame: Blue
Lens: Black
This was my first (and only) pair of M-frames after they overhauled the design. I do like them although they are really tight on my head, which I suppose is a good thing, but they start to really dig in after extended use. I would imagine they work well for biking, motorcycle, and rollerblading. A staple of Oakley's lineup. I think the strike is probably the most popular lens style. Not too big, not too small. I'm sure everybody has at least one pair of M-Frames, if not, get you some.