from my experience, a ring light is the wrong tool for nature macro, and particularly wrong for flowers. a more natural look is obtained from a main source simulating the sky with fill light as required. i find the MT-24ex works well because the two heads can be easily ratioed. i use the lens mount for the fill light, and put main light on an arm. usually use a diffuser on the fill light and sometimes bounce the main light off a small reflector. since the MT-24 works as a controller, you can add a 3rd flash for background.
i find that the basic combination of one light on the lens and other on an arm works pretty well for hand-held flowers (and critters) once you figure out the relative positions and ratios (which is better done initially with a tripod)
i have also used the pop-up flash on my 7D with a Gary Fong diffuser as fill and triggering a 270EXii on an arm - no cord required, but ratioing has to be done with distance and diffusers so there is a bit of trial and error involved
you can also use a larger flash with mini soft box for the main light but this is better on a separate stand
