I thoroughly believe that the competition in TF2 sucks right now but people are better mechanically at the game now than they were before. Mirelin had the best medic mechanics for an older generation of TF2, while knoxx & pyyyour are impressive for pure positioning & their understanding of the game. Indust is impressive for how good he quickly got at understanding the mechanics of medic & probably held the best mechanics at medic when he played, but harbleu was still more impressive IMO.
Shade achieved the most if that's what makes you think a medic is the best.
Mirelin had the best mechanics when he played but raymon ( & many other medics now n days beat mirelin's level of mechanics) holds that now. If mechanics determine the best medic, raymon's your pick.
The last medic I ever thought was impressive to watch was kos.