What would be the closest chinese translation for the last name "Balleto"?

Last names are not translated.

Basically, there is none which matches your requirement perfectly.
Because most of the commonly used Chinese surnames are one character, which have no specific meanings and have only one syllable, and it was inherited from ancestors and will pass down from generation to generation.
"Balleto" has more than one syllable, so you can just choose “bā (巴)”, “báo(薄)”, “bāo (包) or etc. as your Chinese last name.
All these three are not very popular surnames. But, as there are hundreds of Chinese surnames or even more, and none of them has bad meaning, so, as a foreigner, it’s all your choices.

_translation_ would depend on knowing what does the name "Balleto" means in the first place.

_transliteration_ ignores the meaning, and just tries to find a set of characters whose pronunciation sounds close to "Balleto"