Spoken language is the original language. While it may be possible to "get by" without writing it would hardly be possible to do without speaking.
They are both important in my view. People with speech problems still survive in the world using different means of communication such as sign language. :-)
written language is more important in terms of preserving language(s) world wide. It is the oldest and more prestigious form.
HOWEVER, speech is more prolific and there are so many communities where there is no form of written language that to them spoken is obviously the most important. It is also through spoken language that we get linguistic change and dialects etc...##
Hell, I don't know!!
Would you rather live without letters and emails or the phone?
Both have their level of importance, one couldn't do Neither without the spoken nor without the written.