I suggest getting the best you can afford with emphasis on fire protection as well as anti-theft and space.

As far as size goes, my safe is cramped with rifles but I got the best size I could afford. It takes careful effort to remove and put back individual rifles as to not damage/bump, scratch other rifles while removing and putting back other rifles. That being said, get the largest you can afford to have enough room to take out and put back rifles with ease and comfort without doing all the yoga maneuvers I have to with my cramped safe.