I have long believed the purpose of a gun, any gun, was the ability to send projectiles down range with the greatest accuracy and highest level of efficiency possible. That includes economic efficiency. I also hold that certain guns, while not at all economically efficient, are worthy of owning just because--.50 BMG comes to mind. And, there are certain guns that have little practical value except to look pretty, but a combat gun doesn't fall into that category.
Owning a gun solely for its collectible value has never held a great appeal for me. High value collectibles attract thieves and just having something in the safe doesn't do much for anyone.
Everything in my safe is a shooter. Some are sort of duplicates in a sense. I have a couple of .22 rifles--one bolt, one semi--and I enjoy shooting them both. The bolt action is the closest thing to a collectible because it is the very first gun I ever shot at around age seven or eight. It belonged to my favorite uncle and that gun is now nearing the century mark in longevity. It's still in excellent condition. The semi is one of those Remington nylon stock bad boys that shoots 20 rounds just as fast as you can wiggle your finger. In short, it's great good fun.
Any gun you need to get "special" ammo for, or reload with a lighter charge or lighter bullets would seem to me to be a non-starter. The caveat here would be if I suddenly found I had more money than I could possibly know what to do with, I might build an extra room on the house to safe-like specs and buy lots of guns I don't need and wouldn't expect ever to shoot. I do not foresee that condition eventuating.
So, my vote would be for the .308. Good deer gun. Good bear gun. Phenomenal range gun. Reasonable safe queen. Shootable with conventional ammo. Decent price. All the panache you could ask for in an "almost" new gun. And, except for the barrel, the gun has probably seen all the combat you could want.
FWIW,
Crusader Rabbit