We could always use some fun.
Which hero should go "bad" and why? And not just one story-arc bad (a-la Martian Manhunter in JLA). We're talking full-on long-lasting EEVEL (a-la Hal Jordan Parallax). It could be retconned into possession, mind-control, etc., BUT in at least FIVE years.
Conversely, which villain should go good?
People who are "on the fence" (a-la Catwoman) are NOT allowed. Use people who are traditionally associated with good and evil.
1) Aquaman. Let's say the Justice League "accidentally" destroyed Atlantis and Aquaman was so mad he vowed vengeance on the surface dwellers. I can see it. And besides, reading Blackest Night, he is so much better as a villain.
(close runner-up would be Mogo )
2) Tough one for villains. I'm gonna go with Ra's Al Ghul. His "goodness" is sort of like Lionel Luthor's from Smallville. Might be fun actually. Him "helping" Batman and all.
So who's YOUR pick?