Pistol Pete in his prime!!!
His 1 & 2 serve was the greatest, perhaps not the most powerful server but still up there.
He could place them on a dime, Heavy serves that only a PS85 can give you
Have you ever seen a more confident server?
Sure there have been innovators that has raised the bar over the years but if I could choose to serve like any pro past/present... hands down Sampras!!