My guess is City.
City has the financial power to even further strengthen the team. The have the kind of players to play the passing game based on technique. Next, there is the challenge of winning the Champions League, I suspect Pep wouldn't pick a club where there are no great challenges therefore I rule out Milan and Bayern. Also, the technical director or the head of youth is an ex-Barçaman.
I would like to see Pep manage City, I'm not a City fan but if Pep chooses them I suspect we"ll see the emergence of a new superpower in worldfootball not only financial wise.