I have the 6600P and love it for piecing and applique. I have quilted all size quilts on it even a king size with no problem. For the money it can't be beat----I even use the embroidery for my labels----The only down to it is the speed when machine quilting---If your new to free motion quilting it is fine but I got mine after using a Brother 1500, straight stitch and quilting machine so it was a bit of a comedown. I machine quilt my larger quilts on the Brother.
Even with both machines it was cheaper than the other 2 you mentioned. I especially love the stop/start button, which allows me to sew without the pedal--I have fibromyalgia and it is a life saver for sewing when I have pain. Good luck and feel free to PM me if you have questions.