Why an M9 over a newer Beretta like a Px4?

dunno really....liek i said, id use any pistol

While i agree about the px4, Why the fuck would the OP want to carry a 9 in the first place?
They have absolutely NO stopping power.

Well the Px4 also comes in .40 and .45

Primary benefits of 9mm are both the fact that it's very common, and you can carry more rounds per pounds. With slow type zombies the stopping power is of minimal concern, as all you have to do is get the bullet through a skull- which a 9mm round is more than capable of doing. And 9mm hollow points, while not having the stopping power of heavier pistol rounds, allow you a decent amount of stopping power considering that your magazines can pack 17 or 18 rounds. While a .45 1911 holds only 7 standard.

you certainly know your shit, sir.
I suppose i didnt look at all of the possible angles.
I withdraw my first statement.

Whoa....I'd have him in my group....XD

Personally, I'd go with .40 myself. That's what my Px4 is chambered in. I do however also have a .45 1911 and a Cx4 Carbine in 9mm. The 1911 was a gift, and I love it. As for the Cx4 in 9mm, well the ammo is a good bit cheaper and it's primarily for fun!

What about a mark23, the SOCOM pistol in MEtal Gear SOlid 1 and 2.