For me personally, RU over RL every time.
Growing up in Ireland probably had a lot to do with that. I wasn't from a rugby stronghold and never even played club rugby, but there was something special about watching the five nations every February. The 1991 RWC really sparked my interest in the game, and the tournament was a joy to behold, Ireland going so close in the QF against eventual champions Australia, I thought we had won it after Gordon Hamilton's try.
There was little or no exposure to RL when I was growing up. The only time I ever saw RL was on the bbc when the Silk Cut Challenge Cup was on. That has changed since I moved to Australia. RL is everywhere, especially in Sydney. I watch it now and also regularly attend matches. I really appreciate the skill levels of players like Billy Slater and Jarred Hayne, but for me it will always be second to RU.
One of the reasons for this is the difference at the breakdown between the two codes. It's non existent in RL. When a player gets tackled, he rolls the ball back to the dummy half and play continues. There is no opportunity for turnovers unless the tackled player knocks the ball on in contact. In RU the tackled player has to make sure he has support alongside him when tackled, otherwise he will lose the ball or end up conceding a penalty for not releasing.
Another major difference is the scrum. In RL the scrum is uncontested, whereas in RU the scrum is useful for so many reasons. A strong scrummaging pack can win the ball against the head, the can utilise their own scrum to start a rolling maul, or they can break off the back of the scrum to get possession quickly to the backs.
There are no lineouts in RL, while in RU the lineout is a very effective way of setting up backline moves when used effectively. It can also be utilised to regain possession from the opposition.
One thing that really annoys me about RL is that you only get one point for a drop goal. It is one of the hardest skills to master with a rugby ball. I guess it is because the whole point of RL is trying to keep the game moving? But kicking at goal is an essential skill to have, especially in tight games.
Even though there are undoubtedly skillful players in RL, there is all to often players just running into each other trying to use brute force to gain territory. And if that doesn't work they kick the ball away after their set of six.
RU utilises tactical kicking. A good kick can pin the opposition deep in their own 22 with a lineout to come, or it can get you possession back as the opposition fullback often has no option but to kick the ball straight back to you.