Both "bernyani" and "menyani" are correct. In which context would one be more appropriate over the other?
There is a grammatical difference. Although the meaning of both would be "I sing". Saya menyanyi is grammatically incorrect. Me- + nyanyi(transitive verb) requires an object, e.g. Saya menyanyi lagu (a song). Ber + nyanyi (intransitive verb) does not. To just say "I sing" would be saya bernyanyi