Sampras is one tier below Federer, so stop comparing the two.
As for Nadal, he's getting closer and closer to Sampras. Both players have strength and weaknesses. With Sampras it's the clay, too few MS. Nadal has no WTF.
Tier1(goat): Federer; Tier 1.5: Laver, Gonzales, Sampras, Nadal, Borg;
Tier 2: Lendl, Connors, Rosewall, Tilden; Tier 2.5: McEnroe, Agassi