Personally, I love the micron systems. The welds and overall construction is of very high quality and the pipe has a nice deep, throaty sound to it. Now you can get cans in several different colors in both titanium and carbon fiber.
The HMF systems seem to lack the quality I like. The cans don't have that 'finished' look to them with the rivets and welds. The sound is a bit too 'loud' for my tastes, not so much a deep sound. I do like the overall look of the dual-high mount HMF systems, though.