My absolute favorite episode is 57! And for many obvious reasons, but the main reason is because this, honestly, is the only episode of the entire series that I will watch from beginning to end without fast-forwarding, rewinding or stopping!
I love the entire series, but at times when I go back to watch an episode there is a scene I don't like and I will fast-forward it. This is the only episode that I won't do that to! And it is the first time that he called her by her name. And I don't mean simply her first name. I watched the series all the way through, and up until that episode, he only referred to her by name once. Episode 40: Sakura and the Sakura in the Dream. When Sakura, Syaoran, Tomoyo and Meiling are riding in the elevator to the observation deck, Sakura comments, "I feel like Meiling has been calling me all day."
Meiling comments that she's in a daze and Tomoyo comments that Sakura's funny when she's in a daze, and Kero-chan states that both those terms make him worry, but Syaoran intervenes and says, "No, Kinomoto is actually pretty levelheaded." Only time he ever referred to her by her name, and it was all a dream. And that's why ep. 57 is my favorite!