Know-How Exchange : E-Marketing

The answer to your question depends on what the end goal is.

If the goal is to provide a timely answer to the question asked by your user, of what you listed the chat system would be best. Email responses would also be good. These take an inquiry fr.om a customer and give them a direct response. Chat system pretty much requires someone be live responding where email is a little less time sensitive. Plus chat system would have to be set up on your site, where you already have email.
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BLOG and FAQ are slower at answering the initial person's questions, but add a benefit that the questions and answers are published and someone else who has the same question in the future could hopefully find this and get what they need without someone in your company having to take the time to respond (or could be linked to in a response). I look at blogs as better for more complex question/answers - type of thing where more paragraphs would need to be written. FAQs are better for short and sweet - things that could be answered in between a few words to a paragraph or two long answers.