In a fight Hyperstorm fighting baseline Monarch is almost a tossup between the two IMO but post waverider power absorption by Monarch puts him far ahead. I'd go so far as to say it becomes a stomp.
Really? I don't know the character very well (Hyperstorm) I've only seen one appearance of him, and it was when Galactus used him as a sandwich (which begs the question as to why Big G didn't make him a permanent guest in his ship). I also read that Hyperstorm has Phoenix Force capabilities as well as other impressive powers.
He's a Grey family descendant. Also Galactus was trying to use him as a battery that he thought would last him long term. Which is why I say Hyperstorm despite his short appearances should be immensely powerful to be considered a long lasting fuel source for Big G. Like I said I think baseline he takes it in a fight with monarch but post Waverider power absorb Monarch takes this.