I'm trying really hard not to be the guy that comes in and says "NO, NO, NO!! YOU'RE DOING IT ALL WRONG!!!!!" and ruins a decent thread.
That said, "want" (which you used twice in your post) does not belong in the same sentence as "military personnel." Neither does "choice." I can't suspend disbelief enough to imagine that an MP or someone else would be able to choose their own weapon.
You'll get issued either an M9 (Beretta) or an M11 (SIG). And you will get issued that weapon IF you have the rank/duty position to carry one and IF there are enough to issue you one. If you aren't going to a range or actively performing the duty that requires you to carry a weapon, that weapon stays locked in the arms room. Forget about using it as a carry gun.
You might be able to carry your own weapon if you are SF or something. I don't know, I'm not SF. But an MP or something, no way.
P.S. Also, what about standardized NATO calibers?