You could make a good argument for all 4.
My choice: CB Carlos Rogers
As for Clinton Portis, i suspected this might happen. Portis is not the same back he used to be. His decline started near the end of last season and his laziness in the off-season was a recipe for what we have this season.
Santana Moss, well, the horrible shape the offensive line is in, the non-threat of the other receivers, gets Moss doubled up. He has been disappointing in that he isn't not getting open as often and he has had MORE than his fair share of dropped opportunities.
Laron Landry is a mixed bag. One game he looks splendid, the next, he is out of position, takes bad angles, and forget what tackling means. In other words, a heap of inconsistency.
As for Rogers, this has to be the most disappointing. n He has been terrible. In addition, it is a contract year. A contract year! He has self inflicted a loss of millions.