All things considered, I consider Wagner my favorite composer of all time. This is a tiny bit of drivel, but someone pointed out once how a common theme in the Ring cycle and his music seems to be one of unification. I'm aware of how antisemitic the man was, but his music presents something weirdly close to a unification between all people. That aside, I've never heard a composer put this much precision and this much power into their music. Beethoven and Mozart are fantastic too, but their body of work doesn't measure for me. Rheingold Vorspiel is perhaps one of my favorite pieces of classical music of all time. The Solti version is probably my favorite version of the Ring cycle. Oh yeah, that isn't even talking about Ride of the Valkyries. I rewatched Apocalypse Now a few months ago, when my internet was acting up, and the incorporation of it was other-worldly. His orchestra pieces sound like the most insane movie OST ever made in the best way.
Also, here is one of my other favorite pieces of classical music. Just, fucking unbelievable. I remember seeing people on a music forum I frequent praise it to high heavens. It didn't do it for me on first listen, but with each listen, I've grown more and more in love with this. Can't find an official video of the entire thing tho. La sacre du printemps, just fucking unbelievable. That's all I can really muster.