I prefer a variety, some sucking with foreskin forward, some sucking with foreskin back. I prefer they start with foreskin forward. My cockhead is extremely sensitive, and if they immediately retract my foreskin (as I'm forever training fellow Americans NOT to do) and start sucking, I'm likely to cum pretty quickly. As the covered sucking continues, my cock will stretch out to its full length and stiffness, and the foreskin will naturally skin itself back. The you can do whatever you want. (I masturbate usually by sliding my foreskin back and forth over my cockhead, but sometimes I just hold my foreskin forward and slide my fingers up and down the shaft and play with my balls. So many choices when you have an intact cock...)