Stronger words:
* Audacious
* Intrepid
* Valiant
* Gallant
* Heroic
* Bold
* Fearless
* Unflinching
More neutral words:
* Brave
* Dauntless
* Spirited
* Adventurous
* Enterprising
More specific words:
* Gutsy (implies determination in the face of danger)
* Resolute (implies unwavering commitment)
* Stalwart (implies strength and reliability)
* Tenacious (implies persistence)
* Pugnacious (implies a willingness to fight)
The best word choice will depend on the specific context.