My 15-91 is the one my mother got as a wedding present from her parents. She taught me to sew on it when I was 8 years old. She gave it to me when she decided she wasn't going to sew anymore. (Told her that of all the things in the house I wanted was the sewing machine, so she said, "You can take that now.") It is one of my most prized possessions even though it has very little value.
Currently I use my Janome and Viking more than my Singer - but it has to be the most loved. Think I'll sew my next quilt with it since I am thinking about it now.