In a way, backup guns are a lot like cameras, the best one is the one that you have with you. If it is too big, you will not carry it as much, and will probably miss the "perfect shot". I usually carry a 4" Model 66 Smith (.357 Mag) with the old 168 gr. Keith bullet. If there are unfriendly residents with large teeth in the area, I will have my 3" Lew Horton 629.