Depends on the machine. I have a few different ones because what works great on one machine may not work as well on another. I have one like this -
http://shop.sew-classic.com/Low-Shan...luxe-NN-31.htm
and this -
http://shop.sew-classic.com/Low-Shan...td-SCF4021.htm
and this -
http://shop.sew-classic.com/Low-Shan...foot-55417.htm
I even have one machine, an old straight stitch clone, that doesn't like any of the darning feet I've tried so I just leave the regular foot on it. I don't even drop the feed dogs. I just set my stitch length to zero and go.
Cari