Honestly, I do not have that many guns, but I do have more than one or two. I have had a safe for sometime, and, recently, I acquired, rather unintentionally, a larger one. The old one was small and unobtrusive. It has gone to reside elsewhere. The old one would hold most of my long guns. The new one will hold everything and then some. So the question becomes, when you can put everything in there, what, if anything, do you leave out?
The argument for a shotgun is almost overwhelming. I don't expect to need it for self-defense, but it is hard to beat plus it will eliminate most of the annoying varmints and pests and vermin that become a problem from time to time. Perhaps the only argument against it is that I can't stick in in my pocket.
Next would be a handgun because these are easy to pack around when doing other things and can be kept out of sight more easily so as not to frighten visitors unnecessarily. The choice here would probably come down to my XDM .40 or my Super Blackhawk .44. I shoot the Blackhawk better than most of my rifles -- which is not saying a whole lot, but I've improved considerably with the Springfield, and it is stainless when humidity and bad conditions are a concern. Also, I can easily attach a light to the .40's bottom rail to help with those nighttime armadillo confrontations.
Those of you who read this stupid crap of mine fairly regularly can probably guess the next candidate -- my cult favorite, the Marlin .22WMR rifle or the Single-Six with the .22WMR cylinder. In fact, the Single-Six may win out most of the time because a) I shoot it even better than my SBH, b) I don't expect to have to shoot it out with a gang of 'roided up zombie bikers, and c) despite the ammunition shortage I still have hundreds of rounds of .22 mag.
In any case, something tells me I'm not likely to forget the combination on the safe.