I don't have a pfaff, but I did shop quite seriously for one earlier this year. Depending on what you'd like to do with it I loved the 7500 series. Those are any machine starting with 75 - ten years ago they were considered the top of the line and have plenty of doodads to keep a quilter busy for years to come.
Just be sure you understand what the machine does, since these will be used machines each one will offer different things. My mom has an older pfaff not as fancy as the ones I mentioned, as far as I know it's never given her a spec of trouble.
Make a list, write down what you do want in a sewing machine. Decorative stitches? Needle up/down, adjustable presser foot, snap on feet, adjustable stitch length/width, needle threader are just a few things that you might like to have. If you'd like -make two lists, one of MUST HAVES and other of "would likes". That will really help you when you go to the store.