Which sentence is the correct one?

Please help me, I don't know which Spanish sentence is correct:

a) Se lo oyó cantar.

b) Se le oyó cantar.

Thanks in advance.

'le' is preferred in such impersonal constructions, even though it 'should' be 'lo'. This is true in all Spanish speaking countries as far as I know, not just Spain.

Yes, I would say "Se le oyó cantar"

Notice I'm not a Spaniard and it's not leismo, it's just the way it sounds better.

It doesn't matter. Spanish is full of substandard usages.

At least Spanish has a standard unlike English were everything is OK. English doesn't even have something like RAE.

You're right Guest, in English you don't make mistakes you simply "speak diferent"... which will end up screwing up the language even more than it is now.