10-1 Clay to Nadal, depending upon 3 or 5 set. (Sampras would have a better chance @ 3-Set)
3-0 Grass to Sampras. (Sampras's offense was just too fast. )
4-2 Hardcourts to Sampras, depending upon slow or fast HC. (Nadal's worst surface is hard, and Sampras was historically quite good on Hard. Hardcourts don't give Nadal as much time to set up, and Nadal doesn't seem to have as good a feel for hard, nor does he return very well on the surface. Sampras would be able to attack off both his serves. I think that Offense > Defense on most surfaces, and Nadal is primarily a defensive player.)
So it seems overall, according to my analysis.. assuming these surfaces, Nadal would lead that H2H at 12-8.