I use the scant 1/4 in most of the time.
What dictates which you use it the fabric. If a lighter weight or less thread count fab you use the 1/4 in but if a heavier fabric like bitiques you use the scant 1/4 in.
Think you have how many thickness of fabric + tx's the thickness of your thread. If you have a lot of seams in a block it will be off. And a scant seam is just as strong ad the 1/4 in. There is only a thread difference.
You need to make a sample of the blks to decide which one to use before just jumping into the whole thing...
Just a little thing that can make a huge difference.
Happy Quilting