It's not final yet, but City is the right club for him. If he goes to City, he can play alongside some of the world's best players under a manager who helped him raise his game by a few levels and won all the trophies possible. Pep and Messi owe each other a lot and they both know it. It'll be a new environment where he'll still commend lots of respect from fans, teammates, manager and the media.
The Barca board on the other hand can go right back to fucking the club over without interruption. Or maybe there will be a new boss in March and things turn around after. Doesn't matter. Messi should not stay around for that.