In New Approaches to Ranking Economics Journals (or here) the authors rank journals based on citations from a larger sample of journals than has been used in the past, they distinguish overall journal impact from the impact per article and they break down impact into impact within economics, impact within all of social science, impact within policy and impact outside of economics.
When impact is measured by citations from journals within economics, journal impact and impact per article are pretty much what you would expect with the AER, QJE, JPE and Econometrica all scoring highly.
Expanding the citation list to all social science, however, has some big effects especially on impact per article. Most notably, the Journal of Law and Economics has the highest overall impact ranking per article.
Frankly, I was thrilled to see the JLE rank so highly since I have published a number of papers in that journal. Come to think of it, the latter obviously explains the former! Note, by the way, that the citation list does not include law journals so if anything the JLEs impact may be under-weighted.
Kudos must also go to Robert Barro, Ed Glaeser and Lawrence Katz, the editors of the Quarterly Journal of Economics, which is the only journal to rank in the top 5 categories no matter how you break down the data.