I would say either a web diagram or looking for repeated ideas while researching.
If you use a web diagram, you can find multiple subsections of one main topic, and focus on one of the subsections from there.
However, if you look for repeated ideas while researching, you can find more important, focused, and developed information on that one topic to help write your research paper from there.
It all depends on your writing style. If you prefer to write more generally about a topic, I would personally go with the web diagram. If you like to write more detailed on one subject, go with looking for repeated ideas. For this specific question though, I would say looking for repeated ideas is the better option.
