I think that Messi should think of Manchester City as a second option after being free agent in the summer. He would surely prioritize returning to home, Barcelona. However there can still be some hindrances for Messi to go back there. FFP rules in the La Liga can block the way for Barcelona to make this transfer happen. Otherwise Barcelona also wants to sign him again and Xavi also agrees with the board.
If the deal between these two sides doesn't happen then I think Messi should think of Manchester City before PSG - I guess that he wouldn't like to leave Europe soon. Maybe he will need to adapt to a new team again but there is a big difference at this point. The difference is that he can adapt much faster to Manchester City's game plan compared to his first times at PSG.
Because he is already very familiar with Guardiola's system and he can feel like he is playing for Barcelona nearly.
If he can't perform well at his age in French league, its premier league he will perform? messi will not add anything to the manchester city current squad, pep Guardola system in the premier league is differ from that of Barcelona, if Pep Guardola wanted messi he would have bought him, but Pep preferred Ronaldo than messi in the citizen squard. Messi wont be retuning to Barcelona noe would he sign for Manchester city. i feel he will join his rivalry Ronaldo in saudi Arabia for the money and to promote the league too. psg were not just cool with messi performance in the club since his arrival. is good they both part way
I think it would be great for Lionel Messi if he joins Manchester City. But I think Manchester City will not show much interest in adding Messi to the team. Because Manchester City have a great demand for players in their squad. Now we wait for another attraction which team Lionel Messi joins.