I think it's extremely important to simulate the service motion of a top player who uses a simple, basic motion. Then, after a year or so, you can allow that simple motion to evolve to where your own style starts to apply.
In the beginning, you don't know what motion is best, and don't know how to make any motion work, so start simple.
Simple as in PetrKorda for lefties, and StanSmith/MichaelStich for righties.
Fed and Sampras are complicated, take timing, takes legs.
DJ's is more simple.
Nadal's might be too basic, but it works for strong, explosive guys.
Ferrer's good, Verdasco's good, but more complicated with the low drop.
JuanCarlosFerrero and LeytonHewitt some of the best to try to simulate.
Once you have the basic fast first serve and solid heavy spin second serve, you can start to use your own personality into the motion.