I used to play and follow Union, still follow it Internationally, but I was introduced to League back in the mid 1980's with a trip to the grand final at Old Trafford with a friend.  (He came from Wigan but supported St Helens... brave lad. 
As it happens, St Helens ground at Knowsley Road was only a few minutes drive from where I lived at the time and I started to go a bit.  Really enjoyed it, and the fact that I could stand up throughout the game and give it one with the vocal encouragement made it more enjoyable. 
It is a game I really do enjoy when I can get to see it.  I suppose I am a Saints supporter really as it is the team I went to see.