I had to get the word out on a couple of cartoons that I haven't seen listed yet:
Favourites:
Undergrads - I watched this show religiously every night as a teen. It's basically a college life survival guide comedy, that has 4 very relatable main characters, who you've probably known in your life in some form or another. It's actually my favourite animated show that I'm highly nostalgic for. I even had to buy 2 copies of the box set of this criminally cancelled-before-it's-time 13 episode series in case something happened to one copy.
Clone High - A show that I somehow missed in my teen years, that ran close to Undergrads' schedule. My wife introduced me to this show years later, and I was hooked. It's got a similar feeling to Undergrads. It's a little zanier, and deals with High School life, but I still love it. It follows a cast of genetically copied clones of historical figures like Abraham Lincoln, Gandhi, Joan of Arc, etc, as they go about their school year in another case of a 13 episode series that was cancelled before it's time.
Cybersix - Thank you for mentioning this mjmassey! Yet ANOTHER 13 episode series that ended too soon! I loved the art style, music and atmosphere to this show. I get highly nostalgic whenever I think about it.
Red vs. Blue Not traditionally animated by any means, but I've been a huge fan of this witty machinima series for 13 years. I can't wait until season 14. It started off as a very humorous series for it's first 5 seasons, and then branched off into having a very engaging story, peppered with awesome action scenes, while still retaining it's humour for the latter seasons.
And others that I enjoy are Reboot, American Dad, South Park, Rick and Morty (which I've just become a huge fan of), Simpsons (Seasons 1 to 9), Futurama, and...I'm probably going to get maimed for this...but Family Guy. I don't really care what people say. I don't watch the show for deep messages and themes. My wife and I just enjoy the humour, even if it's not everyone's cup of tea. I just don't take it seriously at all. I vastly prefer American Dad though. At least from Seasons 1 to 8.
Least Favourite Shows
Archer - For some reason, everyone I know LOVES Archer, but I just find it's characters and humour very one dimensional. Everyone seems to only have one trait, except for maybe Archer, and everyone keeps making the same jokes about every character. After 9 episodes, my wife and I got bored fast.
King of the Hill - Just...boring. Words can't describe how bored I get watching this show. That's probably why I never stuck around.