I go with Franklin Richards if it is the Celestial Buster adult Richards that has conscious control of his reality-shaping and made a herald out of the deceased Galactus. Neron is essentially the DC universe's devil so in his own dimension I would say, with isolated omnipotence maybe with prep he could just blink Franklin out of being but it would be more to his nature to bargain his soul for souls of his family. Definite curbstomp if Franklin's sister Valeria the genius is able to assist and strategize against the demon.
@OmegaDynasty: The Spectre is often beaten by plot devices and that first instance posted was a prime example. The Spectre being not ever really pleased with being to a human host, it embraced the opportunity presented by Neron. The powerset of the Spectre fluctuates wildly between limitless (classic clash against the Anit-Monitor) to impotent (powerless against the Spear of Destiny in the hands of Cain and easily subjugated into speaking the Anti-Life Equation).
@OmegaDynasty: Impressive, but the Spectre is a big jobber, so I don't take him to seriously.
I dont think you notice, he doesnt fight Spectre at all in the scan, what he does, and if interested its from The Spectre 35, he offers Spectre freedom from human hoast
Jim Corrigan refuses because he feels he is already free, but there comes the twist, when Nero says the freedom deal was for Spectre
The Spectre accepts and leaves Jim Corrigan willingly, as you see in the remaining scans:
So Nero doesnt ever fight Spectre, all he does is offer him a deal, Spectre takes it.
Nero fights Spectre much later in the story arc, Day of Judgement 05, and pwns Nero with a wave of his hand
So thats the full picture, take from it what you will.