Most patterns use 1/4", but if you're doing your own pattern, you can use the 1/2". I use the 1/4" because it's what most patterns require. Then press to the side. I haven't had any difficulty with this except for a couple of baby quilts that the person washed the dickens out of...nothing much would have survived her treatment of them.
Easiest way to check your 1/4" seam is to sew on an index card. Those lines are precisely the 1/4" you need. Make sure you are using the correct weight thread, too...I found out thread width makes a difference. Just say in'.