I have the 6600 and absolutely love it! I found a used one at a dealer. I looked at the 7700 too, but I couldn't justify the additional cost for just a couple bells and whistles that I most likely wouldn't ever use. The 6600 has the built in accufeed system (walking foot) and it is amazing. It has lots of decorative stitches, thread cutter and auto threader which I use all the time, and the ability to wind a bobbin while sewing (I never do that, always wind several bobbins before starting). I can tell you that it won't be a machine that you will be taking to classes as she is pretty heavy. I don't know anything about any of the other machines, but I do know that if you choose the 6600, you won't ever be disappointed.