Hollow points, frangible, or other "tactical rounds" may do much more damage and have more stopping power, but they also have a tendency to have chambering problems, especially in cheap guns. That's why I go with FMJ. Ball ammo is also more likely to get through thick clothing, or an inch or two of drywall, or a car door, so keep that in mind. The 9mm isn't a .45, but it should still have enough punch to discourage those things that go bump in the night. Reliability trumps firepower.

You'll get different opinions from different authorities (gun nuts seem obssessed with causing as much trauma and tissue damage as possible), but I've always felt leery of using munitions designed primarily to defeat the surgeon's art.

There's one more advantage of a .45 (which you no doubt are already thoroughly familiar with). It is a big, slow round which will disable someone just about anywhere you hit him, transferring all its momentum inside the body, instead of penetrating on through and expending its kinetic energy elsewhere; but unless it hits a vital organ, the target will probably survive if help arrives quickly. Most important, the piece is bulky enough you won't be tempted to carry it around with you. It will stay in your room or vehicle where it belongs.