Trading during a major session will generally offer tighter spreads, which can be advantageous to a trader looking to reduce their broker costs. Additionally, trading during the major forex market hours will allow traders to potentially capitalize on higher volatility in the markets, as most of the daily volume occurs during these sessions.

The Asian Session is usually the least active session. However, During the Asian session, Pacific currencies tend to move more. (AUD, NZD, and JPY) 

The London Session is the most active session which makes it perfect for a trader looking for volatility. However, due to it's hours it may make it not ideal for traders living in the US. UK100 tends to move the most during the London session.

During the New York Session NAS100, US30, and SPX500 are heavy movers.