I bought a used Viking Designer (original Designer with D cards) about 8 years ago. My machine is almost 15 years old and runs like a dream. I personally wanted some embroidery (D cards have designs that you slip in and select on touch screen), but I didn't want to pay thousands for that option ... I am first and foremost a quilter.
Things I looked for and got were: needle down position (when you stop to turn etc, needle stays down in fabric. You don't have to lift in the back), free motion quilting with feed dogs that could be lowered, button hole stitch for applique, came with a walking foot, sensor pressure on top of fabric (you can set type of fabric - or use auto) and it senses pressure and adjusts pressure from above to suit the type of fabric, and top loading bobbin.