The Braves walkoff for opening night in 2008 was the best moment of his I was at. I'd say the World Series 1st homer was his most important moment because he set the tone for the series and showed we weren't going to get bullrushed by that hyped about "super" team.
I also think that he's at the "if not now, when?" stage. This team is not contending in 2022, probably not before 2025 and only then if Soto somehow decides to stay. Even in 2020 and 2021, the team had a chance to get back to the playoffs. He could just stay and fade, with the team not willing to tell him when, but he's not going to be here for the next contender.