For me, it depends wholly and completely on the situation and the quilt. If I need the seams to match, usually I press to one side so they nest. However, several months ago I was commissioned to make a quilt, "Night Sky" by Jaybird Quilts. Because it was a commercial pattern and I was making it for a customer, I followed the directions exactly, which said to press seams open. I was glad I did, because there were several seams coming together in one spot and it would have been a nightmare if I'd pressed to the side.