I would favor Steve “Pearls Before Swine" Pastis (sp?). He's still writing them and he still has new ideas.
I found Peanuts being kind of dull and homely as a kid, and was surprised by much sharper humor in his earlier comics; then he found Jesus and apparently handed in his sense of humor, and put Peanuts onto infinite repeat. He was pretty innovative in his early years, including having a multiracial comic when that was enough to get you banned from half the newspapers in the country. (Just having a black kid who wasn't 100% stereotyped was enough, there didn't have to be a message.)
But that's the cartoonists' curse, isn't it? Dik Browne hasn't really made any new jokes since I was in college. Beetle Bailey was already on "new repeats" mode when I was in high school. Bill Watterson and Berke Breathed both stopped to avoid becoming caricatures of themselves, Bill Watterson (Calvin & Hobbes) stopped while still in his prime.