1) Lobo easily since he's killed the populations of entire planets
2) Wolverine probably, but only because of his lifespan. And that's assuming he was killing people his whole life.
Conan & Punisher are probably close. If you look at Conan's long career of killings as a thief, adventurer, soldier, mercenary, and king, he killed a lot of people. More so in the orginal REH stories.
Hulk goes last. For many years I think they stated that despite the destruction he caused, the Hulk's rampages didn't result in any deaths. That changed a bit later on.