@dodirty: I didn't mention Banner because I thhink he might actually be decent, obviouslly as a Hulk fan I have alot of respect for what Bruce Banner is capable of and think he's underrated in terms of intelligence, creativity and will power.
- Spidey would still be a weak Lantern for the reason I mentioned above, easily the worst of the choices here. Love him but Parker would be crap.
- Cap would be strong because of will but has like no creativity and would likely not survive the underhanded situations he'd be put in and die.
- Tony is like the opposite not strong willed but creative as hell, he'd do well until he ran into the more powerful Lanterns where his arrogance would get him killed. He probably wouldn't even bring his suits if he got real powers, seems like a Stark thing to do to say "well I don't need this anymore".
- I've never been impressed with T'challa's showings of will so I think he'd be second worst Lantern here. He can also be hit or miss on creativity, you have all that vibratnium and you choose DAGGERS as your primary weapon?
- Punisher could be good because of his will but as others have said he'd fit in better with the Red Lanterns and would likely be kicked out the Green Lantern core quickly for his brutality anyway.
Honorable mentions who would be great: Nightcrawler, She Hulk, Captain Marvel (Ms.Marvel), Nico (Runaways), etc.
I could likely think of more but this should do it for now.