Historically, Real Madrid has won more El Clásico games than Barcelona.
Real Madrid has won 95 of 235 games, ~40%.
Barcelona has won 91 of 235 games, ~ 39%.
49 games have been a stalemate, ~ 21%.
Image: Adapted from Wikipedia.
However, in the past 10 years in La Liga, Barcelona edges Real Madrid with 3 more wins.
It is always a close and a heated encounter. You can never be certain who will win! One thing you can be certain of though, that Sergio Ramos will get a yellow card at least.