Ren & Stimpy
The Simpsons
South Park
Beavis & Butthead
King of the Hill
The Ripping Friends
Looney Tunes

There are other good ones not mentioned, e.g. Scooby Doo etc, but these I feel do and will stand the test of time.

The first 3 seasons of SpongeBob, Courage, Teen Titans, KND, The Legend of Aang, Ed, Edd, and Eddy, etc.

I don't watch a lot of cartoons these days, not because I've "matured", just because I stopped watching TV in general for a few years now, 4, I think.

Currently my favorite is Gravity Falls, I also like the Faily Odd Parents, Phineas and Ferb, Gumball, Steven Universe and Adventure TIme
When I was a kid my favorites were Sponge Bob, Hey Arnold, Cow and Chicken (I don't know why), Courage the Cowardly Dog, Rugrats (in my early elementary school days and late kindergarten), the Powerfuff Girls and the Wild Thornberrys. When I was a teenager my favorite by a lot was KND Kids Next Door (my favorite from 2005 to 2008) followed by the Fairly Odd Parents and Danny Phantom, I also liked a lot Brandy and Mr. Whiskers,Kim Possible and Teen Titans.

Spongebob, Fairly OddParents, PowerPuff Girls, Simpsons, Gravity Falls, Phineas and Ferb, Courage the Cowardly Dog, Recess, and Tom and Jerry are the best ones that come off the top of my head.

If we count anime, add Attack on Titan and Parasyte