Node content versioning and compare tool
You can use Revisioning module for comparisons of different revisions:


  Revisioning is a module for the configuration of workflows to create,
  moderate and publish content revisions.


or you can use Diff module:


  This module adds a tab for sufficiently permissioned users. The tab
  shows all revisions like standard Drupal but it also allows pretty
  viewing of all added/changed/deleted words between revisions.