The default on my Bernina 440 is 2.4. This is perfectly fine for all but small pieces. Standard clothing is 12 stitches per inch and the 2.4 setting is 11 stitches per inch. I set mine at 2.7 because of my vision difficulty - it makes unsewing much easier for me. If you are paper piecing, you need to use a much smaller stitch or the stitches come out when you pull the paper.
If stitching is coming out, it is more likely to be a problem with how the stitches are being made than the size. Many, many quilts were hand stitched and the fabric often wore out before stitches came out.