I use the 57 for power sewing long strips at high speed, that I then cut into the pattern pieces needed.
I use the 37 for when I have pinned the points on a sewn pattern strip of pieces, and want the points to match those that I am sewing them to. The lack of a guide is helpful for me, in that circumstance. The presence of a guide on the 57 is a help in the other usage. I would say get both of them. If money is a problem and you don't do any power sewing get the 37. My 2cents.
John