the two I use most are the smith 442 .38 special and the midsize glock 40 cal.
But the Ruger Blackhawk .41 magnum with 4 5/8" barrel would be hard to leave behind.
The revolver choice is easy - my 4" S&W 686 Plus .357 Mag.
The pistol choice is much harder. It would come down to a choice between my IA Walther PPK/S .380 and my 4.5" Springfield XDm .45. I'd probably keep the PPK/S for it's concealability - I could easily buy another XDm.