I 9mm is an effective round (for a hand gun). Personally, I don't think you'll go wrong with a 9mm, .40, or .45 ACP. I carry a Springfield XD-S chambered in .45 ACP, and my wife carries a 9mm as her everyday carry gun.
If there was trouble at my house, I'm not going for any of my handguns. Then it's shotgun / AR-15 time.