I learned to piece and quilt on a 6500 and fell in love with it. I then was able to use a 6600P and that is what I ended up buying four years ago. I love my machine. The issues with the machines are minimal and you just learn the quirks of your own machine.
Be sure to use only bobbins for Janome machines. I bought a plethora of them from E-bay and they work beautifully. The 6600P requires one with perfectly straight top and bottom, no concave whatsoever or it will mess up everytime.
I clean the bobbin area after every project or 10 hours of sewing. Use quality thread, mine does not like the cheaper thread so I use Connecting Thread threads now.
Hope this helps.