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I started a new game so I don't have any real map clutter but If you're talking the absolute safest base of all time? (from what I've explored) 2, build a raft and sail out there the land is small, you can't fit too much on it but you'll never be raided in a million years and the only danger will be sharks; but going back and forth is a hassle especially if you're transporting new captives (this can be fixed by leveling transport so you can fast travel with flags)
Base 1 however is on a hill surrounded by invisible walls especially behind it where the arrow is pointing. You can fortify the front of it to make yourself more *feel* more comfortable and they only have 1 path to attack from however most raids come down from the mountain (direction of arrow) at least in my experience and never make it past the invisible wall. So even when you get raided there's absolutely zero danger what so ever.
The cons to each of these areas though is that they're extremely limited on size so you won't be making any massive bases.