I forgot to say which sewing machines I have. I have a Janome MC4800 and a Singer 15-91. My Janome isn't top of the line - but computerized versus mechanical.
Actually, I think the tension is a little off on my Singer. Not sure what adjustments to make - because whatever I do doesn't really change the look of the stitch (well, ultimately it does - but seems to be a fine line between it looks the same as the previous adjustments or suddenly it is clearly off). I think the stitching on the underside of the fabric is often slightly nicer than what I see on the front - very straight, concise.