Formal:
* Meu amor: This is the most common and general way to say "my love" or "my darling." It's appropriate for both romantic and platonic relationships.
* Minha querida/meu querido: This means "my dear" and is a more formal and respectful way to address someone.
Informal:
* Meu bem: This translates to "my good" and is a more affectionate way to say "my darling" or "my love."
* Meu amorzinho: This is a cute and endearing way to say "my little love" or "my darling."
* Meu tesouro: This means "my treasure" and is a very affectionate and loving way to address someone.
* Meu anjo: This means "my angel" and is a very loving and intimate way to address someone.
Other options:
* Meu bem-amado/minha bem-amada: This literally translates to "my beloved" and is a very romantic and passionate way to say "my darling."
* Meu coração: This means "my heart" and is a very passionate and heartfelt way to express love.
Ultimately, the best way to say "my darling" in Portuguese depends on the context and your relationship with the person you're addressing.