From my personal experience, frozen are readily taken while pellets takes time for fishes to recognize as food. In order to lessen the pollution to your tank, you can thaw frozen food in a plastic strainer and discard the liquids.
There are some pellets that are able to provide as much nutrition as frozen food if not better.
Personally, I prefer pellets as I don't have time/patience to wait for the food to thaw.
Recently, I am also trying out a pellet that is supposed to be more envirnmentally friendly. http://www.dragonfeeds.com/index.php?optio...&Itemid=109 drop me a PM if you want some to try.