I didn't read all of the responses below but I have an opinion and that's what 'interneting' is for right?
I like the workshop format when there are a lot of people who either need ideas or want to share their ideas. Lotsa things flying around stick where they are most needed. It's brainstorming essentially.
I like the interview format for focus. "We" are distracted folks these days. I love talking to one person about only their ideas and actions. Then I; or whoever is listening, can distill those ideas into either 1) things that are useful to explore further or 2) things to throw away or just don't apply for me.
However; workshop and panel style convey more ideas in a short timeframe. Interviews convey focused ideas in the same timeframe. So I think it comes down to knowing your audience. Do they need and want a wide array of ideas to chew on or do they want directed opinions and advice?