I can't pick a list because too many players sit on the same level. I could easily put Kolarov, Dzeko, Fernandinho, Zaba, Silva, Nasri, and probably more at number 2. Some were better earlier in the season, some better later. Negredo earlier on was exceptional, and Aguero was one of the top 3 players in the world in the first 15 or so games he played.
Yaya is different. He really is a man at the peak of his powers, and to score not only the amount but the quality of goals he has this season (and that's from someone who hates goals deciding these type of things), it's nothing short of exceptional.