One large one like a Liberty. They are pre drilled for lag bolts which you can use to anchor to your basement. Ain't going anywhere. Plus, they are extremely hard to break into in the first place.
As for smaller safes, never underestimate the strength of a couple motivated thieves. You're worried about banging up your walls going down that oddly shaped stairwell, they couldn't care less. Might take them a few minutes, but also affords them the luxury of breaking into the safe at their place if they just simply steal the smaller safes.