Nihilus drained an entire planet of force sensitives and the entire Jedi council, so I’m pretty sure he can handle Maul. Even without Force Drain, Nihilus still wins IMO. His telekinesis is absurdly powerful (capable of moving capital ships and dominating Kreia or the Exile, Marr, and Mandalore combined). He also is a high-level master in telepathic attacks (enslaved an entire crew including Visas Marr), Force Stun (with the wave of his hand he could incapacitate the Exile, Marr, and Mandalore combined), and Sever Force (also with a wave of his hand he stripped Kreia from the Force).