There's been some valid debate about who is the greater champion, Pete Sampras or Roger Federer.
Comparisions are bound to happen as both them of them had a fairly complete, all court game. Great one handed backhands both, very capable volleyers both. Sampras possibly had a slight edge on his serve, but undisputably the factor that sets Federer apart is his unrivalled domination of the sport.
Sampras was the dominating force in his time yes, but against players like Agassi & a few others, he seemed beatable. Federer's domination of men's Tennis is almost complete!
The above may be debatable, but then one has to consider this:
Sampras finished his career with 14 Grand Slam titles.
Federer has another 5 years left and already has 12 Grand Slams in his kitty! Barring a total unforeseen breakdown of the mind & body that make up the winning machine called Roger Federer, he will set records that will not be broken for decades to come!
But the sealing argument comes from Sampras himself. After the 3 exhibition matches they played, and Sampras winning the third, Sampras admitted that Federer was probably exhausted coming off a long season. He also stated that Roger had things to his game that he himself didn't have in his prime!
I agree with Sampras.