No way has Federer got a better serve than Sampras. Im sick of these Sampras Federer comparisons but no way can i keep quiet about this. Right now I think Fed has by far the most effective serve on tour, but Sampras had the best serve of all time. How often do you see a second serve ace from federer?
Federer does have a better backhand and return. But Sampras was equally good on the forehand side and and his net play would have been his major weapon against fed.
I dont wanna criticise fed, great player, very classy guy, maybe one day he will deserve to be called the greatest of all time, but his serve will never be better that Sampras'.