Lets see.. has any other ninja been able to stop the kyuubi? No. So a technique that can even stop the great Nine Tails can be said to be the greatest, and techniques are only as strong as the user, so you can't really compare it with using it on a tree. A skilled user wouldn't be stupid enough as to use it on a tree, and one who could seal the kyuubi would only need his bare hands to cut down a tree.