Active Voice is usually preferred.
Passive Voice - the subject receives the action and it might have the phrase “by the…”.
Passive Voice is usually avoided except in 2 cases:
- Subject of the sentence is indefinite/general. E.g. Rice is not grown in these fields (good). They do not grow rice in these fields (poor)
- Depends on what the writer emphasises. E.g. America was discovered by Columbus. or Columbus discovered America.