Best swing ever?? Fred Couples has the best swing ever. 2nd isn't even close and that belongs to Ben Hogan.
i'll agree on Rory and Fred.
the common thread being freakish physical range of motion abilities. (flexibility).
i think Freddie was double jointed on top of otherwise being very flexible, and not even other tour players who are freakishly flexible themselves, have the range of motion in their trunk that Rory does. (and i question if Rory didn't lose a hair of that when he bulked up).
before his bulk up, i freeze framed Rory at the top of his follow through one time. the midpoint of his shoulders was pointed almost 180 degrees opposite of where his belt buckle was pointed. (looked like a circus contortionist).
no matter how rhythmic and coordinated and skilled normal humans are, they never will have the range of motion to swing like Rory and Freddie, which is what allows them to have the long beautiful graceful swings they have/had.
and that long swing is what facilitates their power, as it allows them more time/arc to generate speed on their downswing.
it's one thing to go vertical or past on your back swing by hinging more at the wrist and hands and knees.
it's another, to be able to do it with the big muscles in your trunk and back.