I love these films pretty equally.
The first one is joyous, looser and carefree--which fits with the stage Jesse and Celine were at their lives. Before Sunset, on the other hand, is more thoughtful and filled with a greater sense of urgency/poignancy. The ending of Before Sunset is PERFECT.
I love the chemistry between Ethan and Julie. The films are my idea of romantic fantasy. I would love to be able to connect with someone on the level that they do. They really listen, engage and challenge one another. To me that's an expression of love more sincere than what we typically see in more mainstream films.
Judy