Originally Posted by luvsfordpower
It depends on the look you are going for and how you'll sew it on. I would use a zig zag on the onesies because of the stretch of the fabric. Make it a loose zig zag for a little bit of a raggie look, or make it a tight zig zag (satin stitch) for a more finished look.
I made a few of these for my son when he was little, and I ironed mine onto the onesie and then used a satin stitch all the way around.