Nagato had a pretty shitty childhood, but at least had Konan out of it. Gaara at least had his siblings (not much but something). Sasuke had admiration from others, even though he couldn't care less about that after what happened to him when Itachi killed their parents. Naruto didn't really get all that much until a while in, since everyone was shitting the bed about Kyuubi at the time. Sasuke was hell bemt on revenge, Gaara got full on twisted until his tun in with Naruto, Nagato became seeminlgy desensitized after everything that happened, Naruto was the only one who actually seemed sensitive to it all. I suppose it depends on the reader's perspective. Some may even venture to say Obito or Kakashi or even Neji, but meh. I will go with Nagato. He lost his parents and his best friend, and was a war child. Most others just lost a parent.