Well, its better to defrost them before feeding because it takes the fish a lot longer to digest something very cold than something "tank" temperature.
I feed hikari bloodworms, brine shrimp, and squid. I used to have tubifex worms also, but i didn't like the way the fish reacted when I fed them the worms. They didn't like them much, they didn't attack them the way they did with the bloodworms. In the tubifex worms place I now feed squid. They like the squid more than the tubifex, but still, I don't think they like them all that much. I will next try mysis shrimp in the third spot of the rotation to see how they like it.