There was an instant and dramatic improvement in my piecing when I went from an old Montgomery Wards machine to a new Pfaff 2030. You couldn't sew a straight quarter inch seam on the Wards machine, you had to sort of sew at an angle. Even the quarter inch foot didn't help on that machine. It always made a groaning sound with the quarter inch foot on it.
I can't free motion on the Pfaff but I can straight line quilt on it with no problems because of the built in walking foot.