Revolver - S&W 686 or GP100 Too close to call. I like the 4" Redhawk also.
Semi auto pistol - CZ75 SP-01 Far and away best looking semi auto pistol imho.
Single shot - TC 45-70 I'm not very familiar with single shot handguns but I know TC makes a 45-70 so I picked the 45-70 because it's my favorite round. I can only imagine what it would feel like shooting hot 45-70 rounds in a handgun.