A written brief in Supreme Court is much superior compared to an oral argument. A written brief proves to be the primary document from which a judge reads and understands the case. A brief is something which can be carried handy and can be used for future references.
A brief needs to be thoroughly reviewed and edited until it provides the clear outline of the case.
An oral argument can be at times too persuasive that it may bias or influence the minds of the judges and also the attorneys must be well prepared and not deviate from their defense while they present the argument.