It depends on what CPU & mobo you have. Intel SB & IB CPUs cannot directly use over 1600 MHz' but many mobo OEMs can crank out 2133 or even 2800 MHz. If your mobo OEM specs 2133 it may be the best choice.
My CPU is the i5 3570k paired with an Asus P8Z77-V LK. I'm thinking about buying the Corsair Vengeance 2133 MHz 8GB for $39.99