Sasuke FTW. It doesn't get any worse than seeing your all your family and friends killed by the brother you trusted. Naruto's story is sad...he was teased and treated mercilessly, but his personality kept him going. Gaara's story is similiar to naruto's, but he needed naruto's help to get over it. Kabuto's background story is kinda sad, but I don't feel too sorry for him. He still seems like a lunatic to me.