gskills

Hi guys, I have a 2GB Zion DDR3 1333MHz RAM & I wanna increase the RAM of my system.Should I go for a single stick of GSkill's 2GB DDR3 1333MHz or a single stick of GSkill's 4GB DDR3 1333MHz.I only have 2 RAM slots in my Motherboard & 1 is free.I'm not planning to overclock so will...