Whatever gun I haven't shot much lately, unless it has some other value.
(Example: I have a Colt 1917 that was carried by one of Merrill's Marauders; that one stays, even if I rarely shoot it.)
Generally speaking, I don't get excessively attached to objects. This includes guns, cars, trucks, motorcycles. They are things.
I've recently sold a bunch of guns, to finance other things, such as barn improvements. May sell more in months to come, baby is on the way.
Odds are I will not sell the Model 18 I learned to shoot handguns with, my modified Les Baer UTC, my Hunter Customs Commander, my Model 13-3 3", my Transitional Model 629 6", my Savage 99 .300, or my CMP Correct Grade M-1. Other guns in the safe are all potential sacrifical lambs.