I can't narrow it done to one, so I'll list several:
All around favorite is my M27 to .44 Special conversion. The work was done in 1976 and it was my second law enforcement revolver.
My funnest shooting revolver (yeah, I know that's not a word) is a 5" Official Police .32-20.
A .22 LR Remington rolling block fills the rifle catagory.
It's a tossup on shotguns. I have a 1897 Winchester 12 gauge with an 18 1/4" barrel that I carried as a duty gun and now serves in home defense. The 12 gauge Darne double is neat because of the sliding breach block and is a featherweight.