Gajeel solos! since he has his shadows and the Dragon slayers are faster not to mention one punch of Natsu can kill them and end the cycle.
Tho Aang in Avater mode is a danger to them.
@AnimeDefender: Aang never showed blood bending and idk about Korra since honestly I have not watched the series cause the original cast grew in me and them dead is not cool.
so I don't think whey will do that and even if they can, they need a full moon to do so. Unless they can do it in Avatar mode since I am positive they can since they get the strength and knowledge of their previous lives! such as Kyoshi the beast who would smack Gajeel and Natsu due to her awesomeness and cut and pushed a island.