Pick up a copy of the June 2012
Outdoor Photographer magazine. It has an artical about macro flash gear. Basically the artically talks down the ring flashes as creating a flat shot because it creats an even light with no direction. Where as, the twin flashes with a flash brackets allow you to direct the flash to creat depth and fill at the same time. It also gives some flash backet options to choose from. If you do not want the hard copy, here is the web site version of the artical:
http://www.outdoorphotographer.com/h...cro-flash.html