Synonyms:
* Positive: Brave, valiant, bold, fearless, intrepid, daring, audacious, heroic, gallant, spirited, strong-willed, resolute, determined, tenacious, undaunted, self-assured, confident, plucky, game.
* Neutral: Strong, tough, resilient, steadfast, unwavering, unyielding.
Antonyms:
* Negative: Cowardly, fearful, timid, apprehensive, afraid, scared, timorous, fainthearted, weak, spineless, craven, pusillanimous, sheepish, submissive.
* Neutral: Hesitant, reluctant, indecisive, cautious, reserved, passive.
The best synonym or antonym to use will depend on the specific context and nuance you want to convey.