Quoted from Rarehero:While I loved Futurama (mostly...the last few seasons weren't very good aside from a few eps), it's done and gone. It's got a passionate cult fanbase but it never caught on with the masses. South Park on the other hand, is still alive and kicking and is part of pop culture in a way that Futurama never was. It will still be a relevant property as long as it's on the air, and pretty evergreen after the fact. It's a good time to strike on a new SP pin, IMO.
Don't forget that the pc game they made recently, "The Stick Of Truth," was a huge hit. It would make an interesting pinball machine itself!