"Two leading health-insurance providers squared off during congressional testimony Thursday, debating whether the government should allow more plans to participate in the $47 billion health-benefits program for federal employees.... United Healthcare asserted that adding more plans to the mix would increase competition and help keep premium costs in check.... Blue Cross Blue Shield, which covers more than 60 percent of the federal workforce as the sole provider of the program's government-wide 'service benefit plan,' ... is concerned that smaller providers will cherry-pick low-cost regions, ultimately driving up premiums for the nationwide plans."