I consider this the easiest question yet. If you happen to own a revolver in 357 magnum, that is a given. There is no more versatile handgun in usage or ammunition. It can handle everything that a 380 up to a 45acp can do. Between 38 specials and 357 magnum ammo, it can equal all other self defense handguns on the market. Great for home defense or personal defense. The ONLY other gun that is more powerful; but CAN'T go low enough; is a 44mag or one of the hunting revolvers. So in my case:
S&W Model 13-1 4" 357 magnum
2nd gun: Normally I would say that it would be my SigSauer P220 45acp. It is one of the best guns in the world. However; it takes up the same size and such as the S&W 357 magnum. Therefor, there isn't really any advantage to having it. It shoots 8 rounds and the S&W does 6. But I'm not a believer in more rounds in the magazine is of any real significant advantage. Not unless you suck as shooting. So, I'd probably go with a gun that is better for carrying. That would be my:
CZ-82 9mm Makarove or AP-MBP 32acp. I can fit both in my boot, IWB, SOB, or any where else.