The Spain Super Cup will be held in Saudi Arabia, so no team possess the home field advantage.
Valencia have been on fire lately without a loss in their last 6 games, including a 1-1 draw against Real Madrid.
On the other hand, Real Madrid won their last league game against Getafe with 3-0 thanks to another Thibaut Courtois heroics. They are likely to keep another clean sheet in this game. Not to mention that they have Karim Benzema.
Therefore Los Blancos should be supported in this game.