KC or JK. It depends on if you like soft putter plastic or not. I don't, so I voted KC. But that is just a matter of personal preference. Both are the Big Bead mold, which makes them a bit more overstable and predictable.
The Aviar Driver is also the Big Bead in Star plastic. It's nice as an approach disc and short-range driver, but I don't like the feel of Star for putting. Again, that is just personal preference. I have not seen the new Champ Aviar, so I don't know if it is the Big Bead or Beadless mold. Again, I'm not all that hep on the feel of Champ for putting, but if it's the Big Bead I'll pick some up for approach shots and short drives and save the wear and tear on my KC's.