at one's best

English

Prepositional phrase

at one's best

Performing as well as one can.
She’s not at her best in the moming(s).

References

“at one's best”, in Collins English Dictionary.
“at your best” in Longman Dictionary of Contemporary English, Longman.
“at someone's/something's best” (US) / “at someone's/something's best” (UK) in Macmillan English Dictionary.