at its best

at best

1. In the best possible scenario. At best, Doug will be only an hour late. They're only selling junk at the yard sale, so I think they'll make $10 at best.
2. Ideally suited for success. In this usage, a pronoun is used between "at" and "best." I'm not at my best when I'm tired.

at its best

Of or at the highest standard of quality possible. You'll love their new album; it's simply jazz at its best.