Oh, that's easy. Get the more expensive one


Okay, maybe that isn't the best advice. But I have the twin flash and think it is great. I haven't used the ring, but imagine the twin gives more control of which direction the light comes from (and of course you can always remove one of the flashes from the ring and mount it elsewhere). I find it useful to use one flash to fill the background and one to light the subject. The lights are super-adjustable.


One downside of the ring is the twin reflections (two glints of light in each eye of an insect), which can be distracting.