Random routing seems okay if you think only about busy servers under light load. However, one of the problems is it creates light servers when under heavy over-all load. Any time a server is idle during a high overall demand period is work opportunity that is irreversibly lost. I made this argument in the single-thread 2-server case here http://www.win-vector.com/blog/2013/02/randomized-algorithms... , but he principle applies much more generally.