1. Chicago Cubs
In my opinion, it's the Cubs who are the biggest threats to the Cardinals. I think you could make a case that the Cubs should be considered favorites.
I wrote a piece on whether or not the Cardinals should be favorites a while back, making a case for both sides. Granted, the Cubs haven't done a whole lot. They added Michael Busch in a trade with the Dodgers and signed Shota Imanaga, and those are good moves to be fair.
But what makes the Cubs the biggest threat to the Cardinals is the fact that they may not be done. As each day passes, it appears more and more likely that they'll have a clear path to adding another star to their lineup.
Whether it's re-signing Cody Bellinger or bringing in Matt Chapman, the Cubs can't be taken lightly. The frustrating thing is that the Cardinals probably won't do anything big to counter if the Cubs add another bat.
We can only hope that the Cubs are unable to do anything else, but they have the money to do more and are a team that shouldn't be slept on. They came close to reaching the postseason last year after all.
If they do make another big move, then I think they'll end up being considered the favorites in the Central, mostly because the Cardinals appear to be done making big splashes, even though they shouldn't be.