You can try either EURUSD, which is the most common pair that is used by many traders, or GBPUSD, which is also quite promising.
I also use BTCUSD currency pair to trade in during the day. But you need to do your own research and find which currency pair suits you the best.
Imo, this depends on the time zone you are and which currency pair you are trading. It is best to trade the currency pairs at times when they are highly liquid.
i always support EUR/USD due to its comfortable trading spreads. this is also supportive for scalping.
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.