With the development of communicate technology, ways of discussing become increasingly various. In the past, maybe we could only have a meeting when we face d a controversial problem. However, we could send an E-mail, send massages or have a phone call to do this. And among these methods, I hold the point that send E-mail is the best.
First, when we send an E-mail, it provide us for more time to think what we want to say. In this way, we could output our viewpoint with high-quality logically. On the contrary, we do not have enough such spaces by having a phone call. Once, my university wants to cut the facilities of exercise so that it can spent more funds to laboratory, which arise much attention in the campus. There had been a quarrel between people who often exercise and ones who always stay in the laboratory. It is no doubt that they cannot persuade each other. Finally, they sent E-mails to the university office and clearly argued why they think so. Only in this way can they talk with others peacefully in front of a controversial problem.
Also, thanks to the low frequency of communication, people would try to understand what others think, which result in a efficient process. In most discussion meeting or phone meeting, people only emphasize their thoughts over and over but not to listen to a different proposition. If they sustain such a situation, they cannot reach an agreement forever. 
Admittedly, telephone offer us a fast way to discuss. We could get information from others timely. But it is mentioning that we are facing a controversial problem. Telephone can actually make the discussion quicker, but it not means efficiency in fact. There is no deny that such a quick way of communication would trigger a brawl in this case. That is not we want to see obviously.
Thus, sending an E-mail is no doubt a best way.