My top three favorites:
Calvin and Hobbes
Bloom County
The Far Side

Honorable Mention: Pearls Before Swine

 

I'll see your Sid the Sexist and raise you a Fritz the Cat.

Nothing British about R. Crumb. He did somewhat recently illustrate the Book of Genesis so has moved beyond his bawdy early years.

Like Mr. Crumb, I myself am reformed, but not so much as to let a Brit out toilet talk a Yank.

 

For me it's gotta be either Calvin and Hobbes or The Farside.

 

Calvin and Hobbes
XKCD
classic Doonesbury
PhD comics
This Modern World
Peanuts

 

Non Sequitur is a favourite: this is a recent one...