A citation manager helps you keep track of articles and books as you find them, tag and annotate them, and easily create citations and bibliographies in Microsoft Word, Google Docs, or other writing software. Using any citation manager will be more efficient for most scholars than not using one at all.
Even if you use a citation manager, you will still need to consider what citation style you plan to use (even though the formatting with many citation managers is automatic).
All Three Programs Can:
Reasons to Choose EndNote Basic:
Reasons to Choose Mendeley:
Reasons to Choose Zotero: