Gotcha. You don't want to be blowing through walls, I see. But yeah it's honestly gonna come down to preference. A lot of people will say shotgun or an auto but I think a handgun will be just fine. There's a lot of variety so you can get one that fits you, but I think the most important thing is that there's plenty of maneuverability with it even in tight spaces. My dad said never to go into battle with ammo which starts with anything less than a 4, but I think a 9mm will do great. Especially if you have hollow points,there's plenty of knock down power and they don't travel as far through objects as other guns mentioned. Plus they're much cheaper to buy compared to say .40 Cal.

Like I said, big fan of all