They are supposed to perform the same function (i.e. host aerobic bacteria) but IMO
the ceramic media provides a larger surface area and therefore does a better job. I use Seachem's Matrix myself which is similar to ceramic rings.
Gene Heitman - 12 tanks (11 freshwater and 1 saltwater), 206 gallons, 20+ species of fish/shrimp/snails, 52+ species of plants ... 10 years ago I just wanted 1 tank with some fish