That depends on the liquidity of pairs. Some pairs trend better than the others. Traders need to analyse those trends and then choose the pairs they want to trade. Major pairs are more tradeable, in general. Pairs like EUR/USD, USD/JPY, and GBP/CHF are good choices to trade.
I mainly trade EUR/USD, this is the most liquid pair and my broker fxopen has very small spreads (1-2 pips) for it, which allows you to earn even on small price movements. At the same time, this pair moves quite smoothly, is not very volatile, which allows you to set small stop losses.