This competitive showdown just saw one of the players hit a couple of bumps.Eli Lilly (LLY 2.11%) and Novo Nordisk (NVO 1.19%) are big pharma peers. They're also each other's biggest rivals, especially in the all-important market for weight-loss drugs, in which both are currently highly successful.Right now, there are a few reasons to believe that Eli Lilly has the upper hand in this competitive clash. Those reasons support buying its stock, assuming you don't want to invest in both companies. Here are thre ...