Bioshock 2 will always be my favorite of the series
The first game, although it didn't age so well, is still one of the games with the best atmosphere and story I've ever played.
And Infinite, even with several of its flaws, has a very entertaining gameplay and the dynamics between its protagonists is quite entertaining.
But there is something that I simply love about the second game that I'm not sure I can describe that puts it above the other two games in the franchise in my personal taste.