Rushmore was the first movie of his I saw. It has a lot of the Wes Anderson trademarks but he had to do it more on a budget so it was more about the story and characters. I think by now, he just has a greenlight on everything so it becomes more style over substance for me lately.
Royal Tenenbaums is the sweet spot for me for his movies. He had really honed in on his visual style and trademarks, but still had a really good, cohesive story with a great ensemble cast. I still love looking at his movies, but it seems like more time goes into deciding what wallpaper he wants to use than what the story actually is haha. There are some cool (and new) visual elements in French Dispatch which I liked though.