This is such a toughie :) But I have to say to this date, my favorite scene for Delena is the Miss Mystic Falls Dance. Because both Damon and Elena felt the chemistry between each other. Elena's expressions changed towards the end of the dance and so did Damon's. This scene made me ship them 100% because I couldn't deny their amazing chemistry :)
My other Favorite Scenes:
The Rose, I love you scene. Its the best scene of season 2, wish Elena had been able to remember it was such a beautiful confession.
Friday Night Bites kitchen scenes.
Under Control teddy scenes :)
Daddy Issues scenes.
Fool me once scene.
Children of the Damned kitchen scene :)