Federer, but I have an incredible amount of respect for what Borg did at Wimbledon. He is the only player in history who completely changed his natural game so completely for another surface and dominated. Arguably the greatest baseliner in history, coming to grass and serve and volleying on 1st and sometimes 2nd serves, not his natural game at all, and winning 5 Wimbledons in a row, and being nearly as dominant as he was on clay.
It is nothing like Djokovic and Borg who just play their natural excellent baseline only games on now phony rye grass.