Adventure Outdoors would get my vote; I haven't measured it, but they must have 60 to 80 feet of glass display cases/counters full of handguns, with rifles and shotguns of various kinds lining the wall behind the counter (sometimes two levels of long guns, one above the other!). Bernie's is pretty good, but they have nowhere near the selection.
My main beef with AO is that a couple of years ago they started to prohibit carrying a loaded gun inside the store, apparently even for CCW holders, and even if it stayed holstered. Annoys the feces out of me. Because of this policy, a friend of mine refers to them as Communist Outdoors now and tries not to go there.
But they have a big selection.