Selection Criteria

Based on this experience and my preference for open-source software, I've come to place high importance on the following  functionality/characteristics when selecting a reference manager.
  1. Portability so it works across a variety of writing platforms and operating systems
  2. Local and cloud storage for working off-line and synchronization across devices
  3. Multiple import options that include adding items by object identifier, RIS, and BibTeX 
  4. Shared libraries for collaborating with other writers
  5. Cross-folder assignment that allows references to be included in multiple folders
  6. Document upload for attaching 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 freemium price strategy that allows paid or free versions
  10. Intuitiveness because the software should work for the user, 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.  Zotero is a community developed, open-source platform that offers both free and paid levels.  The free level comes with all the functionality of the paid, just with restricted cloud storage.  Your reference collections and user information are as private as you choose them to be.  As a professional platform, some choose to make their information publicly visible, but that's up to you.  Regardless, the platform does not scrape and sell your personal information.  The interface is quite intuitive for a platform with extensive functionality.  And because the code is open source, you can find a wide variety of add-ons to customize the way Zotero works for you.