Also, nobody seems to mention the frames. I have a Tin Lizzie and was having problems with doing small motifs. I finally figured out that it's the frame, not the machine. It doesn't want to do diagonals easily. If I'm doing a big swoopy curve, the momentum is there and it works OK, but at a slower rate of speed and a small curve, it's too stiff. On the plus side, I can stitch in the ditch without a guide :-)
I bought a used set-up, so didn't have an option, but if I had to do it again, I would look long and hard at the frame too.