AUD/USD and USD/CAD are also generally considered majors. As fibonelli says, EUR/USD is generally the most liquid, but liquidity in any of the major pairs (and major crosses) really isn't anything a retail trader needs to concern themself with. There's plenty of it (meaning the ability to readily get in and out of positions) in all of them around the clock. That said, for a new trader EUR/USD is one of the easier to trade.