Formal:
* Meu amor: This is the most common and widely used term for "sweetheart," translating literally as "my love."
* Querido/a: This means "dear" or "beloved" and is often used as a term of endearment.
* Meu bem: This translates to "my good" and is a more informal way to say "sweetheart."
Informal:
* Amor: This is a shorter and more intimate version of "meu amor," meaning "love."
* Vida: This means "life" and is a very affectionate term for "sweetheart."
* Querido/a: As mentioned above, this can also be used informally.
* Benzinho/a: This means "little good" and is a very endearing and affectionate term.
* Coração: This means "heart" and is a very romantic term for "sweetheart."
Other options:
* Meu tesouro: This translates to "my treasure" and is a very special and affectionate term for "sweetheart."
* Meu anjo: This means "my angel" and is a very loving and respectful term for "sweetheart."
The best way to say "sweetheart" in Portuguese depends on the context, your relationship with the person you are talking to, and your level of comfort.