Here, the interviewer wants to gauge the depth of your knowledge when it comes to different messaging channels and how their performance in marketing varies from one to the next. In this case, you will speak only about the channels they've mentioned, SMS and social media, in comparison to email messaging. To back your answer, you can cite statistics from respected industry sources or give an example of results that you have seen repeated throughout different campaigns you have worked on.
This is not the time to talk about customer channel preferences or other factors that drive the numbers you'll mention. For example, you wouldn't want to go too in-depth explaining that a lot of people are easier to reach via SMS text instead of email because it's more convenient to check a text message versus an email. You could, however, want to emphasize the number of customers that are likely to prefer text over email.
