I own both; I've had the 710 since 2005 and have carried it at least 3 days a week ever since. Until the PM2 arrived under the tree last year, that is. Eventually, I imagine the PM2 will lose its luster and it'll settle into regular rotation, but for now I've been carrying it constantly.
As has been said, you can't go wrong with either one. Some observations: the 710 is comfortable in my hand, but the PM2 simply crushes it in ergonomics; the former feels "pretty good" while the latter feels like it was poured in around my fingers and it also gets the nod for retention; as long as your grip is firm, the PM2 simply isn't going anywhere unless your hand goes with it. Reach and confidence in the tip both go to the 710. The Para-Military 2 looks great, but it's also pretty unusual, so if you're looking for a handsome, classic design, I'd pick the 710 there, too. Locks on both are comfortable, strong, and easy to open and close one-handed (at least, for this righty).
As for blade steel, my 710 is 154CM, but to its credit, in 7 years of regular carry and use, it looks almost new and I go a long way between touch-ups. On the flip-side, I've used the tar out of my PM2 over the last 6 weeks and it doesn't need so much as a strop yet -- it still feels like I'm cutting with the factory edge.
Both have great pocket clips, carry comfortably and easily (though the 710 leaves a touch more pocket room), and are rather brilliantly designed. I'm giving the PM2 the edge in overall slicing ability though the 710 wins for penetration, according to my experiences. I don't care for the recurve on the 710 and wish it wasn't there.
Again, considering that you will very likely enjoy either one, I vote for the Para-Military 2, as I like the grind and blade shape just a touch more, as well as its ridiculously comfortable (for me) handle. Spending your money with Spyderco, one of the most upstanding, honest, and transparent knife companies ever, doesn't hurt, either.