This is not a question for which i can give a simple answer. There are different kinds of cartoons out there and if i had to choose one it would be South Park, but, this is a 'grown up' type of cartoons. However we all remember and love those short cartoons that made our childhood lovely. Tom and Jerry, Bugs Bunny, Road Runner. Many more of course and i still watch those whenever i have chance. One part of my life was all about cartoon network and again, i still love this channel. I do not like the CN symbol right now, it looks like some news channel. I remember watching some old cartoons there, like Birdman, Wacky races and the Flintstones. I am a big cartoon fan so obviously i cannot make my pick- Anyway, Tom and Jerry, South Park, Top Cat,Courage, The Jetsons, Two Stupid Dogs, Cow and Chicken, Dexter, Bugs Bunny, TMNT...
And in animated movies category i have to go for Up, Ratatouile, Wall-E, 9, The Iron Giant, etc..
I believe Up is one of the best movies and not just animated, in general.