As a long arm quilter I'd prefer the 1/2" to 1" seams pressed open. Zig zag would be ok if small enough you can still press open. Also a shorter stitch length is ok if it does not cause puckering of the fabric along the seam. Th critical thing is can you easily press it flat and have it stay that way. If you have difficulty pressing it flat you are likely to get back a quilt with some small folds stitched in.