Ruger GP100, stainless steel, 6" barrel.

Powerful weapon, but not so powerful that you can't control it. Extremely durable, built like a tank. Take care of it, and it will take care of you.

Why a revolver? Because they're dependable. Less opportunity for mechanical failure. And if you need more than 6 shots, then you're better off using a machine gun because your aim sucks.