Not all straight pins are created equal. When I go to the store and see packages of “quilters’ pins” I want to scream. Who decided these yellow headed pins were for quilting? These “quilters’ pins” have large shafts therefore making it more difficult to puncture through many layers of fabric. This causes some distortion at the seam lines. I prefer glass head silk pins – 1 3/8 inches with a super fine .50mm shaft. These pins easily glide through layers of fabric and will cause less distortion. The best brand I have found is IBC #5003 from Clotilde.
When hand appliqueing, I use sequin pins. Because these are very small, your thread is less apt to get caught on the pins. I also use safety pins (pinned from the wrong side of the fabric) for appliqueing. Once again, this is to ensure that your thread does not get caught while sewing.
The pin with the white head has a much thinner shaft making it easier to use. (I am not sure if you will be able to see the difference between these pins but the yellow pin’s shaft is much thicker.)