We have used the Swagman Bumper Rack 2 and love it.
http://www.swagman.net/product/bumper-rack-2/
I added some 1/4" flat plate steel 4" wide and long enough for each rack and installed it between the bumper and rack on top and bottom to help keep the bumper from "crushing" My DW has followed me towing with the bikes and she said they do not move at all. I did not want a hitch mount because that introduces "slop" that would magnify each bounce down the road. It was about $75.