You don’t have to pay for it because University Libraries has subscription. EndNote Basic is freely available to UI affiliates and EndNote Desktop is freely available to faculty, staff and graduate students.
If you need to download thousands of citations, EndNote is probably the best tool.
If you work a lot with Web of Science or PubMed, EndNote is probably the best tool since it can directly import references from Web of Science and works very well with PubMed.
If you need access to many different citation styles, EndNote supports thousands of citation styles and continues providing new citation styles upon request.
It’s easier to edit existing citation styles or create your own in EndNote.
Free but there are costs for upgraded storage. If you want to continue to use a citation management software after graduation, when you will no longer have access to University’s EndNote subscription.
If you have a huge number of PDF files in your computer that you want to import into a citation manager, Mendeley works the most smoothly for this purpose. Mendeley’s file organizer can automatically rename your PDFs and file them in a clear folder structure.
If you work a lot with Science Direct and Scopus, Mendeley is probably the best tool, since it can directly import references from Science Direct and Scopus.
Mendeley’s Web Importer allows you to import references from websites and databases into your Mendeley library with a single click. It works well with Google Scholar, IEEE Xplore and PubMed.
The Mendeley interface is probably the most intuitive out of the three citation managers.
Mendeley has social media features that enable you to share your research with a network of people, find out what citations other people are compiling in their libraries, or search Web Catalog which is Mendeley’s crowd-sourced research catalog with millions of papers.