In my opinion its damon

I see where both of them are coming from. It's not black & white, I don't think there is a right or a wrong side in it but that seems to just be me lol

Everything Damon does is from the heart and not something superficial. He doesnt care what Elena thinks about how he is trying to save, he just knows that he WANTS to protect her, not that he has to; Even if he is going about ti all wrong.
To me Stefan seems very superficial. That whole thing about him having her "Respect" was bullshit. The only reason he has her respect is because he lets her do what ever the hell she wants, claiming he wants to PROTECT her. He's just scared that if he tries to stop her froming doing something, it would put there love on the line.

Well, I think both brothers had Elena's best interests at heart. Stefan didn't like that Elena had 'resurrected' Elijah and was scheming with him, you could tell that right away. I think Stefan was too trusting of Elijah, and perhaps too quick to accept Elena's decision. How could he be sure Elijah would forgive them all for killing him twice? Damon at least has the guts to risk displeasing Elena by standing up to her, whereas Stefan doesn't want to chance his relationship with Elena by going against her wishes.

Most definitely damon. For as long as this show has aired, damon has always had her best interests at heart.