Either Leaf or Cloud
Gohan5: The second fanbook suggests that Kumogakure is the most powerful nation because it has the highest overall score of any village. Konohagakure has a population size of five stars, a military strength of three stars, and an economic strength of two stars for a total of ten. Kumogakure has a population size of three stars, a military strength of four stars, and an economic strength of five stars fo a total of twelve. Given this fact and the destruction of Konoha at the hands of Pain, Kumogakure has become the most powerful village.