The health care sector hasn't fully recovered from the shock of President Obama's health care reform. Despite its allure as a defensive sector during a weak economy, health care continues to underperform the S&P 500. But there are clear winners in the space. Express Scripts (NSDQ: ESRX), one of the largest pharmacy benefit managers ( PBM ) in the US, is one of them even if the market doesn't yet realize it. Two major issues have weighed on Express Scripts' share price this year. There is an ongoing contract dispute between the benefits manager and Walgreen Company (NYSE: WAG). And Express Scripts' proposed merger with Medco Health Solutions (NYSE: MHS) has faced intense regulatory scrutiny. The merger would create the largest PBM in the nation, covering about 155 million Americans and roughly 40 percent of all prescriptions written in the US. The economies of scale created by the deal would allow the combined entity to wring huge efficiencies from its operations.