U.S. banks are trading at a 20% discount relative to the S&P 500 (INDEXSP:.INX), leaving more room for price growth as the economy improves, argue Citi analysts Keith Horowitz and Josh Levin, who estimate U.S. GDP growth will hit 2.7% this year and then ramp up to 3% or more in 2015. Regional banks offer poor risk/reward With valuations at 13X 2014 estimated EPS, Horowitz and Levin don’t think that regional banks are attractive investments unless short-term interest rates increase faster than most people currently expect. “We don’t see much near-term upside in the regional banks,” they write. Their…