Clicking on the title of the paper will take you to ArXiv or some other direct PDF source, and the DOI link will take you to the official journal version. Direct PDF links marked (ArXiv vXXX) mean that the ArXiv version differs from the journal version somehow. I try to do a good job about uploading substantial revisions to arXiv, so the differences are in general limited to small revisions that don't really change the substance of the paper very much.