If I had to vote, I'd go for the Janome6600. I have the Janome6500 and love it, don't know if I will ever upgrade to the 6600 cuz I am so happy with the one I have.
Oh, and I love that the Janome has a larger neck area than most other machines. I don't know how much quilting space is available on the Pfaff. That might be a consideration.
warm quilt hugs, sue