At the beginning? Adventure time.
Now? Regular Show.
Adventure time needs to either abandon serialization or brace it, because right now it's making weird art pieces for most of a season and then rushing its story developments.
Finn lost and regrew an arm for no reason, he had a relationship with flame princess begin and end for no reason, ice queen's wife came back and then disappeared for no reason, bubblegum became a kid for a few episodes for no reason. They keep changing the status quo, but they change it back before any good stories are told. What's the point?
Meanwhile, even regular show has embraced serialization, even if slightly. And it's way better for it.
Steven Universe is the MVP though. Great animation, wonderful music, kid friendly writing that doesn't talk down to the audience, and its anime influence really helps it stand out. Gravity Falls is wonderful as well, and it really seems like this season the main plot will have a lot of payoffs.