11-0 Clay to Nadal. Sampras would have no chance against Nadal on this surface, he would had done very well getting thus far to even face Nadal on clay but no he would not win any clay matches against Rafa. He would be aiming to not get bagelled repeatedly if anything.
2-1 Grass to Sampras. (On todays grass it could be Nadal 2-1, being the best returner and capable of an aggressive all court game. But I give it to Sampras for his serve)
3-3 Hardcourts even. depending upon slow or fast HC. Nadal takes all slow hardcourt meetings, and Sampras was historically quite good on fast Hard. Fast hardcourts don't give Nadal as much time to set up but he does return very well on both fast and slow HC.
Overall Nadal takes it 16-4.