Sales funnels are the locked gates to your in-depth info, and a key to your inbound success. The info you are giving away has a small price: the recipient’s name and email address. Different kinds of content will appeal to prospects and customers at different points of their purchasing journey.
When they are simply researching their options, a guide, a comparison chart or something similar would be useful to them. A case study is likely to be read when they are in the deciding stage of their journey.