This is my opinion about why Damon should win Elena:
Damon is a much más complicating character than Stefan. He is strong, intelligent, always wears a mask to hide his true feelings and in the beginning he is being presented to us as the bad guy who is proved not to be so bad after all. In reality, if we look a bit deeper, we will find out that Damon hides much más behind that mask than we know.
One thing is certain: the main feelings are pain and rejection. While still human, Damon was constantly overshadowed por his little brother, Stefan. He loved his mother very much, yet she had to die in order to bring his little brother to life. As a young adult, their father expresses preference towards Stefan, he constantly has huge arguments with Damon who just stands up to who he is, and if it wasn't for Katherine, he would already have kicked him ouy of the house. But in the end even Katherine admitted she always loved Stefan more.
Damon is a powerful vampire and his Power should have been able to provide him everything, all that he ever wanted, but not everything depends on Power. amor is an emotion that is conquered not handed. And when yo amor someone tu give this person the power to hurt tu very badly.
Damon has already felt the pain of lost amor twice, one of the amor he had for his mother, and one of Katherine. One más and he would be destroyed with no going back.
That's why I believe Damon deserves to win Elena más than Stefan. Stefan has never felt so much pain in his life and, yet, Damon can hide pain better than him.
Damon has fought so much to win the amor of Elena and yet she refuses him and tells him she belongs to Stefan. There is no greater pain than unrequited love. When tu amor someone that doesn't return your feelings, it's worse than knowing that the person tu amor has died.
Damon needs Elena. And I believe she needs him too. Not because there is sexual attraction, o because he's hot, dark and mysterious. Because he completes her. Even if she believes she feels complete with Stefan she still can't let Damon go. And a part of her always requires him. She has convinced(or tried to convince) herself that she belongs with Stefan, but in reality she wants Stefan but she both needs and wants Damon.
A relationship that that is formed within two weeks like that of Elena's and Stefan's is never fully complete. It takes time for two people to get to know each other and feel something about each other. In Elena's and Damon's case, Elena hated him in the beginning but later regret it because she saw that there was más to him than she had initially thought. Whereas, in Stefan's and Elena's case everything happened quickly and perfect, they became the gorgeous couple, with no secrets but also no depth. No couple is perfect. It's just not realistic. All the couples are a little twisted and have arguments but when there is amor involved as well, none of those matter. And, to be honest, Stefan made no effort at all to win Elena's heart, whereas Damon fought with everything he had, even his true self, the one that hides behind that arrogant mask.
Stefan would be able to leave Elena if he saw that she was happy with his brother. He would want the best for both of them. But Damon wouldn't be able to mostrar such selflessness(and as we all know, realistic characters are never selfless) There wouln't be a future for him without Elena. He would, most likely, turn evil. Some people think it would be nice if he got together with Bonnie. but I am going to have to disagree. There is no future in a relationship like that of Damon and Bonnie's. From everything we know about the book's Damon, he prefers strong women like Elena not the ones that constantly need saving like Bonnie. Of course there are certain hints that he cares about Bonnie, but they are not enough to make this a believable relationship with amor and I believe that they mostly mostrar how Damon's personallity slowly changes since he meets and falls in amor with Elena, from a cold hearted vampire to a más caring and tender person that even likes humans and don't only think of them as just food.
For these reasons Damon should be with Elena. Because they amor and need each other, notonly have chemistry.
PS Besides when Bonnie cast that spell in The Awakening about Elena's future husband, it was Damon that came in through the door and sat on the chair. He may have busted in but, still, it was him.
They would be the perfect couple.


SPOILERS:
1. L.J dicho that the three last libros are the story of Elena falling in amor with Damon at the same extend that she's in amor with Stefan.

2. I have heard that Damon might turn human in the end.

I'm so looking adelante, hacia adelante to Shadow Souls and Midnight!!!

Please don't be to harsh guys this is just my opinion.