I know I'm giving away my age here, but the TV cartoons really never had much appeal for me. That fact is that most of them are really radio shows with poor quality animation--one of the reasons I enjoy, say, "The Simpsons" is that it is written much like an old radio show, the animation being at best perfunctory.
No, for me it has to be the
theatrical cartoons that really show the animator's art, and that means:
Disney--the king of them all, providing, as one critic put it, "the illusion of life". Even nearly 70 years later, when you watch "Snow White", you can still feel like you are watching an old master painting that has miraculously come to life before your eyes.
Warner Bros--again, the lapse of 60-70 years has not dimmed the wit and sparkle of the works of Friz Freleng, Tex Avery, and, of course Chuck Jones (as well as several other genius directors they had working there

). They were always "edgier" than Disney, which is what made them so much fun to watch, but there was also plenty of art too.
MGM--never so committed to the art as the above were, but once Tex Avery joined them, they produced some real masterpieces. And, of course, Hanna and Barbera got their start there with "Tom and Jerry".
UPA--OK, I never really liked the concept of "limited" animation (I always felt it looked cheap, and it led to some of the worst abuses that are seen on TV today

). However, they
did come up with some seriously important innovations (e.g. the creative use of sound design) and some beloved characters (think of Mr. Magoo
).
Fleischer--sadly, they were always in the "shadow" of Disney, but the fact is that both Max and Dave were true artists and innovators (they invented the "rotoscope" and came up with the idea for the "follow the bouncing ball" singalongs). Their shorts had a truly "urban" feel (as opposed to the "rural" feel of a lot of the Disney material), and they created some truly immortal characters (Koko the Clown, Betty Boop) and did some of best comic-strip adaptations ever (the "Popeye" series and, of course, "Superman").
Finally, though they are not, strictly speaking, "cartoons", I cannot leave unmentioned the brilliant and gorgeous stop-motion shorts of George Pal--I still adore "Tubby the Tuba"
.