All three I like and trade frequently. EURUSD and USDJY have good daily averages and low spreads I often trade for short-term strategies, while XAUUSD with high volatility uses more medium-term strategies.
I like to trade major currency pairs, especially EURUSD because of its low volatility, smoothness and minimal spreads at my broker (0.1-0.2), which makes it possible to earn even on small price movements.