League is simply too repetitive. Personally, I find it pretty tough to sit through an entire match, when you offensive options can be reasonably summed up as four charges up the middle, then (maybe) an outside pass followed by a kick. The only reason the game works at all is because the defense has to give the offense 10 free metres after every tackle. That, and those uncontested scrums drives me utterly crazy. I'd much rather watch a Union scrum be reset a half-dozen times than sit through a single one of the glorified group hugs that League calls a scrum.
Aviva. Rugby league was good but the coaches pushed for too many poor rule changes and ruined it.