A desirable machine is in the eyes of the beholder. We all here have ones we love and ones we don't. There are certain older machines that are popular across a large spectrum of people like most of the pre-1960s Singers. There are those of us who prefer Kenmores, those who like the vintage Japanese machines, some like the really old treadle or hand crank machines, some who like the challenge of bringing the rusty old heaps back to life, some who prefer buying the pristine antique machines, there just isn't any way to narrow a "list" down to a set few machines. It all depends on what makes your heart go pitter patter.
Cari