Verbal communication and written communication are each in their own class. Each of these classes can be equally effective or equally ineffective. The impression you wish to make is largely dependant on your audience size and particular role (That is, are they opposition, neutral parties, or in agreement already?).

Also to be considered is the interest of the audience. If your audience is disinterested then communication is at a disadvantage to begin with and you might enterprise on delivering your communication orally so you can add emphasis and intonation to spice it up. If the audience is already interested and the communication is informative, written words can be used effectively.
Even with this in mind you must consider the ‘type’ of information your communicating. What is the gravity of the situation?

Which method of communication a person opts to use is largely dependant on these factors and then some. There may not be universal answer to the question regarding the efficacy of the methods in terms of which is ‘better’ than the other.