What Marvel or DC character is more ruthless and non hesitant than Jason Voorhees? Is their anyone that compares to this machine of destruction? This isn't about power, this is about agressivness.
Joker works alongside people. Jason would kill anyone that gets close to him without any hesitation at all. I don't think people know how relentless Jason is. He has no friends. He kills whoever is in the vicinity.
You could go with any of the Red Lanterns before Atrocitus gave them the ability to think for themselves, but that'd be boring since they're largely insignificant/unknown. Some Yellows too.
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"And then there was nothing. A once broken something now void.
And on the first day, Doom spoke... 'Be.'
And then there was life."
I'd imagine he plays to many games and has to much varied motivation for his chaos/mayhem. Jason is simple and a pure force of killing intent regardless of victim, surroundings and care for seemingly anything including his own well being. It's why I imagine characters who are capable of brutality and non hesitant murder like black Adam don't really fit the mold and fully qualify as answers to the question. Even they (joker, black Adam) could find themselves in situations where they will hesitate due to various reasons where Jason would hack away with no care.
Not to say Jason doesn't either. as the only thing that I Can remember made him stop was his mother (Freddy appearing as such) but to answer the question as to Whois 'more' a killing machine I'd still go with doomsday who would run over his mother (if he had one) and leave a fine mist in his wake.
Red lanters remind me of attack dogs. They bark and bite at each other but are something to be aimed and unleashed upon. They still recognize a leader and follow orders so I'm curious if they qualify.