I'd go Sage, GB, then Manix. The Sage is just such a perfect knife for EDC, and is very light and comfortable. Thin, light, nice looking, low profile, and sturdy. I've used my Sage hard with no problems.
The GB is very solid and well made, plus the M4 is also impressive. It's just a little bulkier and less discreet than the Sage. I had problems with rust from sweat on hot days though, even with a bit of oil. It wiped right off, so not that big of a problem.
For some reason, I just don't like the Manix 2 much compared to other knives. It's bulky in pocket, plus the cutting edge is short for the overall size of the knife. Something like a Para 2 would be lighter, easier lock, stronger (nested liners), plus thicker blade with less wasted edge. Regardless though, it'll be hard to go wrong. :thumbup: