The pair that matches the strongest currency with the weakest currency. Take the eight major currencies AUD, EUR, GBP, NZD, CAD, CHF, JPY, and USD. Match the strongest with the weakest. If, for example, the GBP is strong, and the NZD is weak, sell the GBPNzD. There is a maximum of 28 currency pair combinations between these majors, and now you know which are the best to trade at a given point in time. Currency strength-weakness analysis is the key.