I think a main theme of Naruto is that the pain of being alone and not being needed, that same pain that Haku, Naruto, Sasuke, and Gaara go through is the worst pain, and it shows the different ways of dealing with it.
With Haku we see that he decides to fight for someone elses dreams because he had none of his own, and wasnt needed until Zabuza came along and finally found a purpose to live
With Gaara we see that the pain of having no loved ones and everyone calling him a monster turn Gaara towards a more evil and twisted lifestyle, that his purpose for life becomes to kill others. He says himself something like "As long as there are people in this world for me to kill and to define myself, then life is wonderful." When his fight with Naruto comes to an end I think Gaara realizes that Love is the power that made Naruto so strong and that the way he decided to define himself was wrong.
With Sasuke we see that because Itachi killed his clan and family infront of him he has devoted his life to revenge and wants to stay alive and get stronger until he can kill Itachi and get revenge. I think the relationship between Naruto and Sasuke will become a deeply bonded friendship and finally Sasuke will realize that living for revenge is not the right thing to do and that "the true power of the ninja comes out when you protect your loved ones" as the 3rd would say.
With Naruto we see a slightly different development that makes him special and what i think makes the anime about him. We see that instead of living to kill others, living for someone elses dream, or living for revenge, his upbringing of the pain of no family or friends and constantly being called a monster has turned him into a ninja who fights for love, who fights for recognition, and who will become very strong when protecting others is at stake. Haku says it early in the anime. He asks Naruto if he has precious friends to which Naruto says yes and that he would protect them. Then Haku says that he will become strong. Its for this same reason that Kakashi had so much confidence in Naruto when he was fighting Kiba because he knew that Naruto fights for the right reasons, that he is a true warrior.
That is what seperates Naruto from the rest, he may be rash, stupid, immature or relying on the kyubi, but it is for this reason that the anime is about Naruto, and even if the pain of the others is worse, i think that all their pains are very similar and that Naruto is the one who will be come the best because of the way he deals with it