In my opinion the best is the moat (or lifting the ground with a hoe around but for this is needed a lot of stones)... natural ground cannot be destroyed by enemies, and they cannot jump. You don't have to build the wall above, a palisade is enough and it is repaired faster if necessary, but of course if you like walls more do it when you will have stonecutter. And when the trolls come, I always leave the base and fight them outside the fence... after all, they don't come to destroy the house, but to kill me.
'Friends' from plains can easily destroy stone walls, not only trolls, but they are not that huge so moat is enough :)