I've always loved Elfen Lied and this song. I also took the time to learn it, but I'm nowhere near as good as you are at it. This is by far the best cover of it I have found.
I'm torn between which sound I like better. I love the tonal differences also. The music box sounds so much more sweet and innocent than the deep piano. But the piano is just as soothing and wonderful. I've thought about attempting to make a cover of this for NG, but I can't bring myself to do it. It's such an emotional piece.