It is cable GBPUSD for intraday trading. Because of the average daily move. You only need to look for the average daily move in pips over a certain time period and then compare it to the trading cost you have when entering a position. On EU or fiber there is much less move per day. Do not forget volatility is your friend when you do intraday trading. You cannot profit from a currency where there is not much movement on a given day. So you can also look for high impact news, if you are a news or momentum breakout trader, when you choose a major pair, because of the expected higher move on this day. Of course it is not easy to profit from red news.