From what I've seen this season Barcelona play better as a team. When some of their starting players are unavailable they still can play with their usual tactical mentality. But when Real Madrid has some missing key players their game plan have to change. So this affects everything about them. Barca don't rely on one or two players. Although Lewa is the most important player, when he's not playing Barca still can find goals. Real is having hard times without Benzema for example.
I think this is the biggest different between these two teams. I believe Barca is favorite right now. Things might change but they are the better side now.