Sampras has the greatest serve ever not because of his 1st serve (there have been many great 1st serves in history) but because his 2nd serve was a major weapon. In the 2000 Australian Open SF vs Agassi, Sampras hit 2nd serve aces twice in the 4th set tie-breaker, one of them 200kph OUT-WIDE and the other 193kph. To have so much skill AND confidence in that 2nd serve under duress like that, is out of this world. It'd be great if someone comes along like that again. Of course, Sampras' 2nd serve is a bi-product of his 1st serve, and some would (wrongfully) say they are identical. What if a player has a relatively weak 1st serve (perhaps flat without a lot of penetration) and a penetrating (via kick or slice) 2nd serve?