Consider 4 different playing surfaces (hard, clay, grass and carpet), and your fav's strongest skills in the following variables:
First Serve: Wayne Arthurs, man he is good
Second Serve: Pete, especially those kick ones....
Volleys & Overhead: Pat, of course
Forehand groundstrokes: Marat, I GOT POWA
Backhand groundstrokes: Chang, i like him
Speed and footwork: Lleyton, though run like a girl though
Mental will and strength: Pete...once a champ, always a champ
Return of serves: Andre, isnt that why he's still "hanging" around
Intangibles (Unusual shots, dropshots, lobs, fear factor, etc...):
probably Andre Agassi, great shot selection i've gotta say....