For me it's kind of an off choice: the Fleischer Studios 'Popeye' shorts from the 1930s. Unlike most other cartoons these took place mainly in gritty, urban settings. They also featured some of the most beautiful and thoughtful animation ever created. People and items have weight, throw shadows, and move perpesctively through the frame.
Here's a good example: 'A Dream Walking' with Popeye and Bluto trying to save a sleep-walking Olive Oyl, but predictable spend most of the time fighting.
The way the beams subtly shift to show weight, the prespective animation as the elevators move up and down, the timing - and just watch as Popeye monkey bars throught the building and marvel at the work that went into the way the beams shift perpective with him.