My fish love brineshrimp, but wont eat silversides, or krill for some reason. I have 2 clowns a firefish, and a lawnmower blenny. I've tried cutting the krill into bite sized morsels, but my clowns injest it, then immediately spit it out.
So for my fish it's a combo of frozen brine shrimp, formula one flake, and blood worms.
I think it depends on what frozen food you are trying to feed.