#1 Manchester City
The team who has got no fear in splashing cash provided that the coach thinks that the player will fit. The current rumors in Spain have put the tug of war for Isco, between City and Juventus, which ends up as an upper hand for the Citizens when it comes to paying astronomical figures.
Manchester City's style of play under Pep Guardiola will benefit Isco a lot. He could assume a role in his strong zone than having to adapt to a different one, which is likely if he plays under Allegri. There is no need to change the balance of the team as well.
If Kevin De Bruyne and Isco play in tandem in the midfield, it spells danger for the opposition of all sorts. With a genius like Guardiola in charge, we can only think of what he can do with Isco at his possession. Better still, Isco could be the long-term replacement for David Silva who is on the wrong side of the thirties.
Guardiola likes a player in every attacking area viz. the right and left wings, the right and left half-spaces and the central zone. Isco could operate in either of the half-spaces and left wing. It gives the coach a better freedom to rotate his team even when De Bruyne returns. This is the best possible option if the star man wants to leave.
Possibility: Highly likely according to rumors in Spain
Pros: More squad depth. The player is a perfect fit at the club. Could help in keeping players fresh during exhaustive schedules.
Cons: No specific weaknesses appear with Isco joining Manchester City.