What pistol do you own duplicate(s) of?
Nearly all of them, because "any pistol worth having is worth having two (or more) of".
Mostly it's so that you have
one to shoot, one to carry. (In practical terms you still shoot the CCW gun intermittently in order to ensure reliability and consistency, but you don't have to always be cleaning the EDC gun.)
Over a period of decades, this has resulted in duplicates of many different guns in my case.