In particular, the Große Fugue [0] and the Op. 106 Hammerklavier sonata [1] (ironically so nicknamed, because at Op. 101, Beethoven directed that all sonatas from that time on be named Große Sonate für das Hammerklavier, and the nickname only stuck to this) show a profoundly advanced sense of counterpoint and structure. In addition to applying all of the classical transformations to motifs (including augmentation, diminution, cancrizans, canons and sequences), he even performs note for note reversals in time. (A temporal cancrizan, if you will.) [Edit: it would be a crime to fail to mention the late string quartets, which show prescience of modernism and are considered to be the pinnacle of chamber music. Many of you will at least be familiar with the Op. 131 c# minor quartet, which Wagner called the "saddest music ever penned" and whose 6th movement was used in the Band of Brothers episode "Why We Fight".]
Similarly, Brahms' masterful applications of form and counterpoint put most other composers to shame. Rather than be as enormously prolific as Bach, the quality of his output is more consistently excellent. (No doubt partially due to his penchant for burning the manuscripts which he felt were subpar.)
I think it's a little unfair to put Bach on this pedestal. There's plenty of music by any composer mentioned to relax to or feel stimulated by. Additionally, Bach's musical temperaments are somewhat limited by his media and styles. He is the master of his craft, but his craft has limited scope.
Yes, Bach has his own, unique, immovable place. But Beethoven, Brahms, and many other composers have immutable, unchallenged championships in their own arenas.
[P.S. Please mark this with a [2014] tag to denote when it was published.]
[0]: https://en.wikipedia.org/wiki/Gro%C3%9Fe_Fuge
[1]: https://en.wikipedia.org/wiki/Piano_Sonata_No._29_(Beethoven...