Based on this experience and my preference for open-source software, I've come to place a high importance on the following  functionality/characteristics when selecting a reference manager.
  1. Portability so it works across a variety of writing platforms
  2. Local and cloud storage for working off-line and synchronization across devices
  3. Multiple import options that include downloading by object identifier, RIS, and BibTeX 
  4. Shared libraries for collaborating with others users
  5. Cross-folder assignment that allows references to be included in multiple folders
  6. Attach documents for adding pertinent files and notes to references 
  7. Open source code so the community can audit the program and develop additional functionality 
  8. Good faith operations that exclude collecting and selling the personal information of users
  9. Reasonable price preferably a feemium price strategy that allows paid or free versions
  10. Intuitiveness because the software should work for you not the other way around
Most of the major reference managers check the boxes on 1-6 quite well, although some do particular tasks better than others.  It's the addition of 7-10 that makes Zotero an outstanding reference manager from my perspective, and my preferred choice.  I've been using a paid version of Zotero for about six years and consider it an invaluable part tool for my teaching and writing.  The free version comes with all the functionality of the paid, just with limited cloud storage.

Putting Zotero to Work

This section covers the basic functions of the Zotero program.