Both, of course! It is customary to start out with the foreskin up and do the things you mentioned then gradually retract it as you get into more vigorous work. However, the essence of a great blowjob is periodic changes of pace. After you've been working on the guy's dick for a while it nice to pull his foreskin back up and play with it as you did when starting.
Besides the things that you mentioned I also like having someone take the tip of my foreskin between his or her lips and pull on it. When I was a young 'un pulling on my foreskin was enough to make me cum right quick. My foreskin is long enough that it covers the head even when fully erect; I don't know if this will work if the foreskin is not that long but it might be worth a try. The bit of the foreskin closest to the frenulum is also a bit of a hot spot so be sure to try making that the spot that you pull on. This spot is still sensitive for me even when the foreskin is retracted but in that case is about halfway down my dick. When the foreskin is down that point can use some nice juicy lip and tongue action.
The frenulum is the hottest spot on my dick. I've talked to guys with partial circumcisions (where the frenulum is left uncut) but none of them had any sensation in theirs. I don't know if this is because of the rest of the tissue that was cut away deadens it or if some guys with intact dicks also don't have much sensation there. It's good to keep the frenulum in mind even when your guy's foreskin up since you can stimulate it thru the skin (suck it thru the skin, put your tongue on the skin over it and rub). It also responds to being pulled with lips and being rubbed with lips and tongue with the foreskin down.
Another area of an intact dick that is sensitive is the intramucosal ring or ridged band. This area is also sensitive to motion and pressure. I did not become aware of this region until recently and haven't had much chance to explore it with a cocksucker. You're probably hitting it pretty well with the things you do for a normal blowjob but it might help you to be aware of the area and what it likes so that you can make sure you are giving it the proper stimulation. Keep your lips in contact with the shaft even after they have gone past the head. Don't just slide up and down, clamp down a little as your lips pass over the ridged band and see how your guy likes it.
These things work for me anyway. Even if they don't work with all uncut guys they should give you some ideas of things to explore. I'm trying to work out a get together with a gay uncut cocksucker, hoping that he knows some more tricks to make my cock happy. If he does, I'll post them here.
If you don't know the anatomy of an uncut dick see the pictures and descriptions in the following link.
http://research.cirp.org/pix1.html