It was a difficult decision, but I would have to say Mello. Some would say that rather than being completely alone, he had Matt, but I honestly don't think that they were all that close. Mello had an amazing personality, and was very intelligent and hard-working. In "Another Note", you see that he is very smart, well-spoken, and even insightful, and forget the reckless, selfish, and immature side. Sadly, his inferiority complex towards Near lead to the distortion of his personality, and it all became that second side that was shown in the anime and manga. That is what lead to his carelessness, as well. He really seemed to understand people, but alas, no one understood him. I really liked the scene where he gave Near information about the Death Note, implying a warmer attitude between the two of them, and that they could have worked together and became friends (which I wish could have happened). With a good friend, they both could have been a lot happier.

Mello isn't selfish. He shared his chocolate with the Shinigami Sidoh for 1 thing.