I prefer a small single action in a big caliber. I love the .45Colt for this purpose (back up gun) because you can load it up or down depending on what you might expect. Commercial rounds are also available if you don't reload (I don't) from the likes of Buffalo bore, Corbon and others. You can get them loaded to .44mag levels or powder puff plinking stuff and anything in between.
I picked up this little Ruger Vaquero Sheriff Model in .45Colt and it's just a sweet shootin six gun, you don't even know it's on your hip. It even packs away nicely in a ruck sack.
