>>723358802 (OP)
recently beat the remake, so I've no idea if it's different in the original.
the butterfly felt bad the few times I used it, but the killer 7 felt way more impactful, but I only used it a few times, and that was mostly on the final boss.
The remake doesn't give enough ammo for it and most of the time I would rather be making shotgun ammo or rifle ammo as ranged attacks felt more common than times I needed to punch through something with a magnum. It cost way too much gunpowder to make the ammo type. As far as I've been told, you could buy ammo in the original RE4, so maybe it's better, but in the remake it costs way too much gunpowder to bother crafting. I recall having more magnum ammo in Re2/3 remakes.
I ended up using the initial pistol and the riot shotgun for most things. the knife upgrade was also extremely valuable.
TL:DR
Killer7 but both are a bit of a waste or a resource trap, at least in the re4 remake that is how they felt.