Marlow has begrudging respect for Kurtz but contempt for the manager.
Explanation:
In Heart of Darkness the whole journey is a lead up to the meeting with Kurtz who has become a larger than life figure in the narration by then. Unfortunately he is taking his last breaths by the time Marlow is there.
Still, Marlow understands that he was a brilliant man who fell to his darkest vices in a place where he should not have been.
For the manager he feels that he fits right in with the darkness as he can keep up his appearance even as he sees inhumane things happening around him.