which phylum is more complex-the sponges or the cnidrians?

Answer 1

According to UC Berkeley's paleontology website: "Cnidarians are said to be the simplest organisms at the tissue grade of organization; their cells are organized into true tissues. Cnidarians are essentially bags made of two cell layers. "
And they are known from an earlier part of earth's history than the sponges (Porifera) (url #2).