I cant stand doing them semi-supinated - seems to take the emphasis away from my tris.
A lot of the big guys (I'm not big enough to calss myself as big yet!) seem to favor the barbell for going heavy because the dumbels can slip out of the groove easily and cause an injury.
I love to do the barbell standing and the dumbell seated. I think that they are both important for a bodybuilder, and should think that doing something like 3 weeks of each alternated would be a good plan.