That's a tough one as I think about it. The characters on American Dad are great and Roger the Alien.... What can you say about Roger that hasn't already been said? But someimes I do find Roger a bit much... I would like to see more of Klaus the German-accented talking fish. I guess, in the end American Dad and The Clevland Show are sort of like apples and oranges.
The style of humor is different. In American Dad, the father, CIA man Stan is funny without seeming to realize he's being funny -- oblivous humor. I guess oblivious humor drives that show.
Cleveland, in keeping with the times I suppose, knows he's funny and lets the audience know he knows they know he's funny. I guess... inclusively ironic humor drives that show.
They're both great shows and I love them both. But I suppose if I was stranded on a desert island with only bread and water and single change of clothes I had to keep washing everyday, with the only book I had to read was a out-fo-date Reader's Digest, and I could only watch one cartoon I would choose......
I'm with you, brimancandy, I woud give the slight nudge to American Dad.