For me there wasn’t just one specific Damon moment that was the best. This whole season reflected his best. From the first episode to the last Damon’s best reflected that no matter the situation, his emotions, his anger, or his hurt - he would always be there for Elena. Not only for Elena but for the whole of Mystic Falls and the people they all care for. I’m not saying that Damon was perfect from beginning to end. There are always some mistakes along the way, but the Damon we saw in Season 4 portrayed the evolution, the progress, the better man in Damon Salvatore. He never gave up in Elena Gilbert - even when he felt there was no hope for them, even when she insulted his love for her when she had no emotions, even when the chance of a human Elena could destroy the possibility of their future. It was all for her - all to give her a chance to survive the way she wanted - the way she deserved.
“Yeah, well…one day you’re going to realize that you don’t know me half as well as you think.”
Why this flashback as a final bonus day appreciation set? Well that quote says it all. The best way to appreciate him is by reflecting on these words because it’s perfectly Damon. Damon is not just one sided, one trope, one type of person or character. He’s so multi-faceted that even his own brother doesn’t truly know him. Part of the audience fails to see this as well. So this quote is perfect because it tries to open the eyes of us all. No one truly knows Damon as well as they think they do. Not even Elena - but I would even say sheprobably is the most aware of the multi-dimensions and beauty of Damon Salvatore.