Formal and literal:
* Ange gardien: This is the most literal and common translation. It's appropriate for most situations.
* Ange protecteur: This emphasizes the protective aspect of the guardian angel.
More poetic or metaphorical:
* Ange tutélaire: This is more poetic and emphasizes the idea of guiding and watching over someone.
* Gentil esprit: This means "kind spirit" and can be used to refer to a guardian angel in a more metaphorical way.
Ultimately, the best way to say "guardian angel" in French depends on the specific context and the desired tone.