Well, what would the the ring help with that the Power Cosmic already can't do by itself?
I don't think it would somehow stack in power as some might say...I'd just wager the ring would become obsolete. Maybe a Lantern's experience with the ring would allow them to be more quickly at home with the Power Cosmic. That might be one advantage.
If I were a GL, or any other sentient being, I'd never be a Herald to Galactus, for one he screws with your soul, and for two, you lose your genitals. You can't tell me that Norrin still has his boys.
To answer your question though Kilowog would make the best physical specimen, because without the ring, he is still super human, and the PC would most likely make him more powerful physically than any average Green Lantern, barring Sodam Yat (is he dead or alive?)
I would think that the ring would help make the PC more dynamic in it's usage, much like the Quantum Bands, maybe to the point that it would amplify the GL/Herald.
I'd definitely go with Kilowog as my choice unless Sodam Yat is still alive. yat would be the most powerful Herald ever imo.
the PC would enhance the GL physical attribute and maybe multiply the ring power output..maybe the GL doesn't even need to recharge the ring anymore..and i think Yat would be the most powerful herald if he is chosen..
If a gl had the power cosmic...
You'd have instanteous cosmic awareness.
(one look at an opponent can tell you their weakness like when surfer faced gladiator)
Massive durability... So if you get past his shields you still have to get past his natural body..
Basically you make a thanos level character
__________________ Quotes from Hia8:
"I claimed that the science is sometimes faulty."
"You don't understand. This is fiction. That means none of this stuff really happened."
"There is no writer to purposely ignore a character's natural ability just because it suits the story."
"in some cases because the writer knows that Character A will dominate Character B easily and refuses to allow this to happen for the sake of the story."