I have a Singer 237, its a simple machine and works well. It uses a 15x1 modern needle and metal class 15 bobbins, needle goes in flat to the right & threads left to right.
My machine is run by treadle power, it came to me with a stretch motor belt that was too small and ruined the motor; thus it became a treadle machine. It was only $20, nice having a zig zag treadle. It was made in Italy and only offered as a treadle there, has a deep groove in the handwheel; so no modification is required to treadle it.
I have done FMQ on several baby quilts with this machine, does it very nicely too. You can see my machine here:
http://good-times.webshots.com/album/578828743YiOtbl
Sharon W. central Texas