I prefer the Manix blade shape a tad more, but the compression lock of the PM2 is easier for me to use. Then there's the issue of weight. The standard black G10 manix weighs about an ounce and 1/2 more than the PM2. However, the sprint run versions and the new s110v G10 version of the Manix 2 have milled liners, which cuts almost an ounce out of the overall weight. The LW version is of no comparison as 2 ounces in that size of a blade is pretty awesome(I cant get used to FRN handles though).
Probably doesn't help in your overall decision. Ive owned variants of both, and I still have my PM2's. The Manix 2's have found other owners, so there's that. Honestly though, you can't go wrong with either one.