All of their albums are so different. Most seem to have themes since the late 90's, and are coherent. Their early stuff was all over the place. For me, Chocolate and Cheese is the turning point, the go between for their two errands. It was a structured all over the place album, if that makes any sense. They proved that they had grown into legitimate musicians, but each song was different from the last.
They've made some amazing stuff since, but that album will always be their apex, as far as I'm concerned.