Formal:
* 最好的朋友 (zuì hǎo de péngyou): This is the most literal translation and means "best friends" in a general sense. It's suitable for formal occasions or when you want to be polite.
Informal:
* 死党 (sǐdǎng): This is a more informal and closer term, similar to "BFF" in English. It implies a very close and loyal friendship.
* 铁哥们 (tiě gēmen): This is a term typically used for male best friends and implies a strong and unbreakable bond.
* 闺蜜 (guī mì): This is a term used for female best friends and emphasizes their closeness and shared experiences.
Other options:
* 知己 (zhī jǐ): This literally translates to "soulmate" and implies a very deep and understanding friendship.
* 知音 (zhī yīn): This translates to "someone who understands you" and emphasizes the mutual understanding and support in the friendship.
The best way to choose the right translation depends on the context and the specific relationship you are describing.