Any SS only machine should have a "true" straight stitch and should do what it does with top quality. A machine that has a movement in the needlebar (any zig zag machine and other stitches) will always have slight movement in it's stitching. SS machines usually have an encased needle bar that's locked in, so there is no swing. Personally, I don't think it matters. I get the same results with a SS or multi-stitch machine.