I think I'd vote Enel, as he seems to have a few more ways to take her down. In terms of AP, Livewire seems to scale to 1.14 megatons and Enel to 1.54, so they're about even.
Enel is always intagible, so Livewire has no way to really hurt him, his Haki, agility and skill should let him handle anything she'll throw at him, and he is also much more experienced both with his abilities and in combat, given the longer time he's had his abilities and how he actually keeps up with the likes of Zoro and Luffy, while Livewire has seemingly dealt with the heroes through raw strength and abilities.
Livewire in turn might be able to absorb Enel's attacks, but that isn't his only way of attacking and unlike Enel, Livewire needs to actively turn intangible, leaving her potentially vulnerable to well-aimed physical strikes.
It'll surely be annoying for both, given all their resistances, absorptions, intangibilities, teleportation, flight etc... especially in such battlefield. Livewire could possess Enel's staff, but he can also do the same and wouldn't be much bothered by it. While unlikely, them running through Metropolis and causing widespread destruction might expose Livewire to water, something to which she seems to be much more vulnerable than Enel, especially on mere touch.
Through feats alone, although both are missing clear explanations and examples, Enel seems to have the higher one, given the length of his fights, the punishment and his ability to restart his vital functions at critical times.
All in all, while it won't be easy for any of them, I believe Enel has ways to outlast her and cause real damage, while Livewire lacks any reliable way to deal any to him.