What's the greatest animated series ever to air on television?S

Animation can create amazing images and ambitious storylines that live-action just can't compete with. Some of our favorite TV shows of all time have been animated. But what's your choice for the absolute best piece of television animation?

Please include a picture or clip of this televisual masterpiece. And please mention the name, and why it's so great. Thanks!

Top image: Batman: The Animated Series.