i think sampras is the greater champion because he had a much harder group of players to play against in his day: edberg, becker, agassi, courier etc. all true legends of the game, federer has a lot easier pool of players: safin (mr inconsistent), hewitt (has lost his fire), agassi (age), nadal (only like to play on clay)...the top 10 today is a lot weaker than in the early 90's.
besides which federer has all the personality of a soggy piece of cardboard.