What Os would be best for me for gaming?

Hello, my question is witch operating system is best for me for gaming. My specs are: and athlon 64 dual core 2.4 ghz (4600+), 2 gb of corsair xms2 ddr2 memory, ati radeon hd 5450 512 mb gddr3, and a seagate barracuda 500 gb SATA 2.0 hard drive. I will be playing mainly games like cod mw2, dead space 2, bf2, bf bad company 2, and burnout paridise.