maybe as far as bacteria goes bio balls work as well be live rock houses all sorts of little creatures that help act like a CUC eating organic matter where bioballs do not. LR
also doesn't have to be cleaned from all the detritus that can build up on them, the little critters that live in the rock do that as well as your actual CUC.
bioballs work no doubt and for a fish only system i would probably go with them over live rock. they are cheaper and just as effective but in a mixed reef the nitrate levels are just to high for most corals to be happy