Which of these struggling hydrogen-driven companies is a better buy right now?Plug Power (PLUG -5.29%) and Nikola (NKLA -4.21%) represent two different ways to invest in the nascent hydrogen power market. Plug Power sells hydrogen fuel systems for electric forklifts and other warehouse equipment, while Nikola develops semitrailer trucks that run on electric batteries and hydrogen fuel cells.Both stocks initially attracted a stampede of bulls. Plug Power went public at a reverse split-adjusted IPO price of $ ...