Runners-up: Red and Rover, Family Circus (again the dialogue is awkward, a real five year old would not throw in the line about beating dad, he would just ask mom to play), Tank McNamara
And here we have an example of good dialogue. Tony Cochran sets up the joke well. The punchline is subtly implied in the last panel. And the dialogue, while certainly unusual, is believable.
Runners-up: Doonesbury, Watch Your Head, Baby Blues, Lio, Brewster Rockit: Space Guy!
Metanote: I had a debate with myself while I was preparing this post. I thought Family Circus was the funniest comic in the paper today. But it was funny in a schadenfreude kind of way, because Billy is going to be scared because his dad won't play with him. In the end, I decided this does not count. The strip is funny only because it is bad, and that does not reflect well on Bil Keane.