This seems to do a pretty good job at comparing, as far as a feature matrix, three of the top repository managers for Maven.
I know for sure developers from Nexus and Archiva have made sure this is up-to-date.
Wall Street Journal Guide to Understanding Money and Investing (Wall Street Journal Guide to Underst by Kenneth M. Morris
Agile Modeling: Effective Practices for eXtreme Programming and the Unified Process by Scott Ambler
Same Kind of Different As Me: A Modern-Day Slave, an International Art Dealer, and the Unlikely Woma by Ron Hall, Denver Moore