Shouldn't be any contest, has to be Gaara. While Naruto still was an outcast/orphan in time he had people who believed in him. Sasuke wasn't totally alone in that he had a purpose to guide him (being an avenger and killing Itachi) so depite lonliness he had that to hold onto.

Gaara on the other hand not only had neither, but what was done to him was completely unjustified. He never asked to be the ultimate ninja, and he never asked to have the Sand bound to his body. He was just a normal kid that wanted normal things, and then those were denied him. And then his whole world was completely shattered when he inadvertently killed Yashamaru and learned everything he was told by him (the only person Gaara thought cared about and loved him) was a complete and utter lie. And that shattered his mind and mutated him into the monster he is now.

There really shouldn't be any contest, as the poll shows.