hands down when sewing through really thick layers, my vintage Kenmore makes the nicest straight stitches of any of my machines followed by my vintage White. For sewing through just two layers of quilting fabric like when piecing, the winner is my featherweight, followed by my sort of vintage Brother VX560.
My PQ 1500s excels at FMQ as does my Brother VX560, both are easy to get tension just right when FMQ. For accurate 1/4 inch seams I use the PQ or the featherweight since they are SS only with center needle position and narrow feed dogs. The Kenmore or the Brother VX560 are left homing needles so they make beautiful stitches, but it's a little harder to be consistent with seam width on anything narrower than 3/8"
both th of my modern machines (the PQ1500s and the PC420PRW) make very nice SS, but even when tension is perfect, they just aren't as pretty as the ones my vintage machines make.
Rob