Elena.

Stefan only had a dark-side in 1920.

The song talks about accepting one's dark side.

That's most definitely Stefan.

Elena, and everyone else, still accepted him... with his dark side even though he was a blood-lusting, Ripper.

The song is like "will you accept me even with my dark side?" It fits bot of them... but ultimately it fits Stefan better because he wants acceptance and he needs it for himself too. Damon wants Elena to accept him the way he is, but he decided he wouldn't change for anyone, kind of putting off an attitude like he doesn't care what they think. Damon knows he's bad and he's accepted it; he wants Elena to too though. Stefan needs to accept himself and needs acceptance from the people he cares about too.