Selecting the best or most appropriate finding aid for identifying sources depends almost entirely on the context of your research assignment. There is no single database or web search interface that will work for every research context; instead, you'll need to match your specific research needs to a variety of options.
Library catalog searches (i.e., Primo) can be the better choice when you are seeking in-depth, book-length treatments of a topic.
Multidisciplinary databases (i.e., JSTOR) cover a wide variety of subject areas and may include a mix of popular and scholarly sources. They can be the most appropriate choice when you just want to get a sense of what's available on a topic and when it isn't so important that you pay attention to disciplinary lenses.
Subject databases (i.e., MLA International Bibliography) cover a specific discipline and provide the widest range of access to scholarly sources. They are used for in-depth research. Which subject databases you search will be determined by who may be writing about your topic. Recommended subject databases for each discipline can be found on the "articles" tab in each library subject guide.
Primary sources are original, uninterpreted information. They vary from discipline to discipline, and are often found in archives, special collections, and museums. See the Primary Sources page in this guide for starting points to this kind of specialized research.