In answer to your question, I myself prefer to use content ferret. It not only helps me to create great content based upon the keyword, but is a great tool for brainstorming too. I prefer to see an entire article around the topic, I am wanting to create content for.
However, saying that, using Answer Analyst, could also be a fantastic tool to help create the right drilled down types of questions, and what you want answers for, again great for coming up with endless niche topic ideas.
I guess, the choice between the 2 would have to be cost. For many they want a tool, that gets updated, and typically pay for it one time. I paid for content ferret as a one time tool. So in my opinion, I would say start with content ferret if you already know the niche. Use Answer Analyst to explore unlimited niches. Now, Article wizard is a bonus with Content ferret, and is an excellent tool to use together with Content Ferret, so the need for Answer Analyst may not even be necessary at that point.
Hope my anwers helps those who read it.