I prefer the 2 square overlay method. I generally draw the sewing line on each side of the center line. My squares start oversized (finished size + 1") and then I cut them down. It is a bit more work but worth it for me. I do QSTs the same way. I believe I cut my squares finished size + 1 1/2 (or even a little bigger).
Some ladies at a retreat I went to, had a ruler that allowed them to trim the HST when it was folded, so they only did one cut. I believe it was a Bonnie Hunter ruler but am not sure.