I have 2 favorites right now, a Pfaff 60 treadle(straight stitch only) & a Bernina 930. I regularly switch out my full size electric machines that will fit in my Horn Quiltmate II cabinet: Bernina 930,1031,Pfaff 1222E and HV Sapphire 875. It depends on what I'm sewing. They're all my favorites.
I have 3 Singer treadle cabinets and 6 different machines that will go in them. I do quite a bit of quilt piecing with a treadle, its relaxing and quiet; I can sew late into the night and not disturb anyone with a machine that has a motor.
Sharon