The big currencies in most peoples estimation are the US dollar (USD), Euro (EUR), yen (JPY), pound (GBP), Swiss frank (CHF), and the Canadian and Australian dollars (CAD and AUD). Therefore, there are 6 major pairs where USD is mixed with any other of the majors. Cross pairs are those not including USD, eg CBP/CHF.
These are the best forex pairs for a retail trader to concentrate on. Generally, if a broker offers any minor currencies for trading, the spread will be high. The exception could be a broker will be offering the currency of their own country at competitive rates even if that currency is not a major. This is especially true for secondary currencies like the New Zealand and Singapore greenbacks that are close to making it into the majors in terms of daily trading volume. First, there’s a lot of competition between brokers so the spread is generally lowest for this pair. 2nd, the high liquidity means that there will often be less slippage, and you are more likely to get the price that you see on screen. Third, foreign exchange reports alerts have a large amount of reports about these currencies so you aren’t so likely to get caught out by unexpected press releases. If you’re using an expert counsellor or FOREX trading robot, on the other hand, it could be set up for other pairs. If that is so it’s best to use it according to its settings. That will not work so well on any but the suggested pairs, so those will be the best forex pairs for an expert advisor.