They're both part of my top five, and clearly are columns in their own right. I think the question which one changed history more than the other. Think of all the post-Wagnerians you have - Bruckner, Wolf, Mahler, Strauss, Debussy, Pfitzner, Schoenberg, and to an extent Italian verismo. What noteworthy composers did Brahms influence? Elgar, Dvorak, and Schoenberg. Not nearly as many, and given that Wagner's cromaticism led to atonality, Schoenberg's second Viennese School either would have been completely different or wouldn't have existed.