This is not a "favorite" player poll, rather who is in your opinion is the strongest and the reason behind it.
I will set the format first. Remember, these are simply opinions, they are meant to illustrate what each of us has problems with now, for me - it's returns. So my opinion may be evolving around that.

R. Federer
Why? - Fast, FH is unplayable.
Best counter: I think the best would be either Isner or Raonic. The serve can take you all the way up to tie break, where a good gamble can payoff.