This may be useful, if you haven't come across it already
http://www.treadleon.net/sewingmachi...ngtreadle.html
If I only had room for one machine I would like to have one with reverse stitch, two of my vintage singers have this feature and two don't. I really miss it when sewing with the two that don't have it.
Another consideration is the "newer" singers (1960's) electric machines, the ones that can also be treadled, then you have the option of zig zag stitching etc.