I'm biased as I've played Union all my life. League Centres around running straight and hard so you have much bigger collisions, much bigger tackles and requires much more fitness as the ball is in play for longer. There's more intricacies to union - props winning scrums, locks in line outs, flankers at rucks and the backs are usually operating in less structured, more broken play which in my opinion makes it more exciting. In league everyone is spread across the field in quite a structured manner and the excitement only comes in the final moves to score tries IMO. Admittedly there are some seriously impressive wingers out there in league, especially in the NRL.