I have avoided this thread for a awhile because of the word "best" in the question (and fellow 'goners know how I feel about that Pandorian word). Without a desire to change the direction of this thread, had I been asked from a "favorites" point of view I would have answered it in terms of some of my favorite rock engineers, those that I feel truly pioneered new directions and approaches to the craft, they would be, in no particular order:
Eddie Kramer
John Leckie
Glyn Johns
Geoff Emerick
Butch Vig
Andy Johns
But, of course, I was not asked that question.