Any gun? I'd want an armored bus, lots of gasoline, several crates of 7.62x39, an AK47, and the "Welcome to NYC" sign receding quickly in my rearview mirror.
Has to be a handgun? I'd go revolver, .357 Magnum, 6" barrel, either a stainless Ruger GP100 or S&W 686 Plus.
- 6" barrel provides better sight radius, and shouldn't be a problem since the SHTF and I don't have to conceal it
- Better ballistics at longer ranges than many other handgun cartridges, such as 9x19 or .45ACP
- Plenty deadly at self defense ranges
- Ammunition should be plentiful as it is very common
- Will shoot 110gr standard pressure .38's, 180gr .357's, and everything in between
- No worries about FTF or FTE issues; just about any bullet type will do, standard to exotic
- Should you run across another .357/.38 revolver (also common) you'll already be packing ammo for it
- Easier to shoot than a .44 Magnum (at least for me)
- I don't know, but I bet either gun is already legal in NY state, and maybe NYC
My GP100 is very fun to shoot, too. YMMV.
jmm