One job for two employees. Which one would you retain?

I have a decision to make… I have two employees that work for me and do basically the same job (accounting). Due to some special circumstances, I can only retain one. Employee #1 is an A+ employee as far as her job duties but she has a horrible attitude. She constantly talks behind my back, never says a positive word and always is critical of any decision I make. Employee #2 is probably rates a B at her job duties but she is a great team player with a great attitude. She always cooperates and gives me a 100% effort at all times. I can only retain one of them. Who would you retain?