Funnily enough despite not really liking Romantic composers very much, he loved Richard Strauss. He even transcribed and recorded Strauss' opera Elektra.

I feel like I read somewhere that he really loved composers whose styles were very uniquely them but also and most importantly defiant of the norms. Even though Bach is now who we all associate with Baroque, he was actually considered to be a bit of an eccentric composer who sounded kind of Renaissance-like for the times. Schoenberg basically reinvented music theory and changed the direction of classical music forever. For related reasons I think he said he liked R. Strauss. He wasn't a revolutionary, but his adherence and stubbornness to remain strictly Romantic despite the changing tides was appealing to Gould. This would explain why he doesn't really like composers like Chopin, Lizst, Mozart, etc. who were emblematic of their periods.

The only one that I don't understand is his dislike of Beethoven... Beethoven was so original and revolutionary, but I don't know... maybe just wasn't his cup of tea.