Ok speed is required if you are overclocking, for overclocking 1600MHz is recommended other wise your RAM could limit your overclock. So go for 1600 if you plan on overclocking (which you should). If you are sure that you will not be overclocking or are on a strict budget then go for 1333, you will still be able to OC a bit.
Latency is important for performance but don't spend too much for lower latencies, stick to your budget but for example if different RAM is the same price with lower latencies then go for that one.