I'm teaching my 9 year old son how to serve properly. I'm big into technique, so I pay close attention to mechanics.
Notice Roger's elbow on the trophy pose:
Fed's elbow sticks out back a bit (due to coiling before his ball toss), and his right elbow is in line with his shoulders (after his tilt back).
Murray, on the other hand, does not drop his right elbow as much as Fed:
Janowicz, also, doesn't seem to have quite elbow drop as Fed:
Is there an inherent advantage to Fed's lower elbow at his Trophy position. He is one of the most accurate servers in history. I'm wondering if this has anything to do with it. Or, can both approaches work equally well?