This is such a personal choice. If I guage this by what I actually listen to, Beethoven overwhelms this list for me. After Beethoven, I don't think I would have a ranked order, but neither Brahms nor Tchaikovksy would be in my top 5 - probably top 10, certainly. Mahler, Sibelius, Wagner, possibly Chopin, Haydn, Dvorak and others are top contenders.
Curious about the person who posted Holst - I have a project on my to-do list to spend a bunch of time listening to Holst past the Planets. I have a handful of other recordings, but mostly he seems to be a one-hit wonder. I have heard of people owning 30+ recordings of the Planets and no other Holst.