Over the Course of Their Entire Runs So Far:
South Park >> Futurama >>> Family Guy > Simpsons
South Park has always been funny depending on your tastes, but in vastly different ways. I think it's much better now than it used to be.
The one or two episodes I've seen of Futurama's newest run have been good, but not as good as the originals. The movies were pretty bad.
I think everyone will agree Family Guy's not the show it used to be, and now the good episodes are hopelessly outnumbered by bad ones.
The Simpsons hasn't fallen nearly as fall as Family Guy has, but it's been going on as a shell of its former self for much longer, so it gets last.
At Their Peak:
Family Guy > Simpsons > South Park > Futurama
These were all hilarious at one point or another. Just at least two of them aren't anymore.
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Ace Detective in Sir Chris' Police
I assure you, my dear, all Ace Detectives are perfect gentlemen!