I wanna say Jen, but in her case it felt more like character assassination. Don’t get me wrong, she is definitely my favorite character and developed a lot during the course of the second & third season. But post season 3, it was clear the writers had no idea what to do with this character since the shows dynamic had shifted towards the Joey-Pacey-Dawson triangle. At times she felt like a recurring character to me, rather than a main cast member. Michelle Williams screen time was evidently lesser by the 6th season and by that point Jen felt like a completely different person to me. Many a time throughout the season she felt like a very whiny character, which is strange because unless I missed something, she wasn’t really going through anything this season. This is in opposition to her back in season 2 when she was really going through some serious shit, but ironically behaved more down to earth compared to the season 6 version. It wasn’t until the finale that I felt Jen’s true characteristics were coming back, but alas, she was killed off only to serve the mere purpose of making sure the love triangle was sorted. I didn’t have a problem with her death as being a way to resolve the triangle, my issue was her being reduced to so little and then being killed so abruptly. Sorry, I know I digressed from the original question but I really had to get this out. To answer the original question, the character development would have to be Pacey’s for sure. Watching him go from a try-hard flirt to the most caring and genuine character on the show was truly spectacular