I've read some of Valery's writings, so far I'm not sure what to think of him. Maybe because the translation takes away some of his style, but my French isn't good enough to understand complex poetry, so I needed a simplified version.
Hesse is interesting, I like his poem "Ich bin ein Stern". And I'm not sure which Mann you mean, I like Heinrich a little better than Thomas, because he's more concrete and entertaining instead of just dwelling in himself the way his younger brother does. TBH, he's an easier read. Less artsy, maybe, but equally interesting, seeing that he offers a different perspective on the same topics.