Please note, EndNote (Basic) is freely available and is the official software supported by the library.
Each of the other listed "free" product has advantages, disadvantages, and quirks but mostly provide the same features. You can easily export your data to another program, but not without some inconveniences.
One key consideration for which tool to use is collaboration. How easily can you share not only your reference folders but actually work on the same document with a colleague? As an EndNote campus, we recommend this software, but you are free to choose any software you want - or use more than one depending on your needs.
To learn more about the features of individual software packages, consult the handy comparison charts provided below, talk to colleagues, or check with Library staff to learn more about your options.