I think it comes down to PSG, United then Barca
this on the basis of salary then playing time. PSG will give him the world plus if they say to him either thiago silva or marquinhos will have to be dropped to make room for you, then it's a done deal. he'll win french titles and get champs league every season to add to his resume.
United clearly need him so it's a dead cert for playing time. will they give him sanchez type wages given how that went? that remains to be seen
someone will be in his ear telling him, barca can still be on the table in 5-7 years (using pique or fabregas as examples, although different scenario as both academy players and catalan/spanish) plus there's a lot more added pressure and competition