For me, playing against the computer inevitably results in me finding a repeatable way to beat it. If there is a story and varied environments, that is acceptable. However, for a real challenge, I’ll always go for human opponents.
Ultimately, you know you can't be one of the best players of the game unless you're around 18 and play the same game 50 hours a week, and you also aren't paired up with completely random players, so you can't really even get real feedback on how much better or worse you are than the average player, since games group you in with players similar to you (but will sometimes change that if it wants to slip you that dopamine to keep playing and hand you an easy win).