Simplicity; to me that implies the old K.I.S.S. theory. I find the Singer 66's to be really good at that. Perhaps it's because they are so very similar to other machines I have have and have been exposed to I don't know.
Modern sewing machines, are like automobiles: way beyond reason complex. I don't think computers have any legitimate place in either. I guess that makes me an anachronism.
Joe