I will respond to this cos I didn't take part in the last debate.
Basically, there should be no League vs Union. They're both great sports; the two greatest 'winter' team sports in the world. And they're brother sports. I cannot understand the hate there is between them; I think a lot of the time it comes from overly tribal people who don't take enough time to learn about the other.
Union is the most pure and all-round code of football there is. The whole game is a contest for posession, you have tall guys, short guys, fat guys and quick guys; kickers, tacklers, magicians... the whole hog. It's like the team version of mixed martial arts - any array of techniques can be combined.
League is more limited in this respect. However, what League offers is a more refined version of the game. The average League back will have a better footballing brain, slicker hands, and generally a higher skill set. The average League forward will be a better ball carrier and a more physical tackler (partly because of the laws...). But League players don't have to think about the breakdown, scrum, lineout or any other technical areas that Union has.
I like to think of the difference as similar to that between Test and T20 cricket. The Tests (Union) give you the pure, extended, high-intensity version of the game. The T20s (League) give a higher level of skill and more instant excitement. Both are fantastic.
I happen to prefer both Union and Tests, but that's not to say I won't follow and watch the other. In fact, that's the best thing about Super League taking place during the Summer - I can now watch rugby 52 weeks a year![/b]