I have a Pfaff 130 in a cabinet and think it is great. It is my "go to" machine. Last year the motor went out, and we replaced it with a lower power compatible motor, and it is still strong. There was someone who posted on this site a few years back who said she used a Pfaff 130 with a hand crank on her sailboat and mended/sewed sails with it.
I have never used a Singer 237, so do not have an opinion about it. However, I do use a 301 a lot of the time, and enjoy it immensely. It does not zigzag, but it sure does sew fast.
If you are looking at a Pfaff 130, I recommend checking the link drive on it (viewable from the underside). It is made of metal and canvas, and if stored in questionable environments, the canvas may be deteriorated. My 130 was pre-owned by a farmer who bought it at an auction sale. The canvas on mine is in perfect condition.
Dayle