#1 Lionel Messi
La Pulga Atomica is the greatest goalscorer in El Clasico history. However, the problem for Real Madrid has been that even when not scoring, the little magician has continued to play a starring role for his side.
His movements, dribbling, and passing has so often created many chances for his teammates to score/created space for moves to be made. Such has been his influence on the games that a significant number of the yellow (and red) cards Ramos has accumulated in Clasicos has been as a result of his tackles on Messi.
Unlike Ronaldo who has become primarily a goalscorer and penalty box assassin in recent times, Messi's role as creator and orchestrator has seen him more involved in the play than his great rival.
While Ronaldo's 18 Clasico goals is a fantastic record, often times, his non-involvement in play has allowed the Catalan side certain freedoms that Real Madrid has not been afforded due to Messi's presence.