I'm still learning Spanish, so I could be wrong, but I believe that "yo lo ví" is the correct answer. The reason is that "lo" is for direct objects and "le" is for indirect objects. In this case, because it's "I saw him," "him" is a direct object. "Him" would be an indirect object if there was another direct object in the sentence; for instance, "I wrote a letter to him" would be "Yo le escribí una carta" because the direct object is now "a letter."

In my opinion, more or less both are correct! "lo" is used in everywhere (or except Spain), but "le" is used mainly in Spain. "Yo lo vi" is the formal way to express "I saw him", but in Spain people prefers colloquially saying it to be: "Yo le vi". This is called "leísmo", a preference for using "le" instead of "lo" when the direct object is a male person (= un hombre). "Leísmo" is very popular and usual in Spain. It is pretty different from the Latin American Spanish, which few people would use "le" instead of "lo" as the direct object.

La forma correcta es "Yo lo vi" Se acepta "Yo le vi" cuando te refieres a un hombre como curiosidad, se escribe "vi"

'Yo lo ví' is the only acceptable answer, according to the DRAE. This is because 'him' is in this instance a direct object in this sentence. We cannot see 'something' to him (contrast with 'I send a letter TO him'.), so we must use the direct object pronoun 'lo'. Hope this helps! *it's worth noting that in many parts of the Spanish speaking world you will hear people saying 'le veo'. This is called 'leísmo' and is very common in colloquial speech, and is actually allowed by the DRAE in the Valencian community of Spain.

Ambas formas son correctas en su pronunciación, escritura y significado. Yo lo ví es común en Latinoamérica Yo le ví es común en España