Which players over the years you have seen had the best service actions.
Good question. I'd have to give that one some serious thought. There are a lot of very good motions out there. The two that come to mind quickly are Sampras and Federer. Those are easy. But a guy like Fish has got one of the smoothest and most efficient motions you'll see.
Querrey has a smooth relaxed motion too. I would have to think for a while to come up with what I consider to be the best motion(s). I think Borg might have had the loosest arm I've ever seen, but he was not really known for serving. But his arm was like spaghetti it was so loose and relaxed.