The only one of those that I would bother to get is the 12 1/2" square. It doesn't have to be Quilt in a Day either. I prefer Deb Tucker's rulers. I think the key to getting a quilter squared up is to learn to press well and OFTEN as you make the quilt, being sure to PRESS not IRON, so you don't pull your fabric out of shape; as someone said, square as you go, although you do have to be careful so you don't keep squaring and it ends up smaller than its supposed to be ; and when you are squaring the final piece, you need two sides that are long enough to let you be sure you are cutting an accurate squared corner. This is why I don't think those smaller rulers do as good of a job. The 12" square is a good tool for this purpose. Plus, you WILL get better the more you sew. The most important thing in the whole process is to HAVE FUN!