Beef ages, so it comes down to your preference, and the cut. As Tom Mylan, executive butcher and co-owner of the local, sustainable butcher shop The Meat Hook in Brooklyn, NY, explained in The Atlantic:
During wet aging, the plastic doesn't allow the meat to breathe, so it ages in contact with its own blood, which lends it "a more intense sour note and a more bloody/serumy flavor," according to the Department of Food Science and Nutrition at the University of Minnesota. This sounds a bit negative when you're talking about the flavor of a steak, but the fact that upwards of 90 percent of the beef taken home by American grocery store shoppers in plastic-wrapped foam trays is wet-aged seems to suggest that it can't be all bad.
Dry aging, on the other hand, allows the meat to breathe, lose water (which increases its "beefiness" since there is now less water and but the same amount of muscle fiber), and get acted upon by other microbes beside those of the muscle itself. Those other microbes are the long, threadlike mycelia of various airborne fungi that begin to digest the meat, giving an aged loin its distinctive flavor, aroma, and fuzzy exterior. So dry aging wins, right? It's complicated: while most meat snobs (myself included) prefer dry-aged beef, the American public actually prefers bagged beef according to a number of very expensive meat studies. Certainly you could chalk those results up to Americans preferring what they have become used to and choosing bagged meat over the funkier flavor of dry-aged beef.
Ultimately neither method of aging is the be-all-end-all: it is impossible to properly dry-age steaks like the flat iron, skirt steak, or chuck tenders because they lack the protective fat and bone that cover traditional aged cuts like rib and short loin. Once they are removed from the carcass, they simply begin to degrade and dry out, which is why I think everyone agrees they should go into plastic.