1 - Kisame
2 - Tobirama
3 - Mei
4 - Second Mizukage
5 - Suigetsu or Mangetsu
Personally, I don't know what is the big deal in making water out of air moisture if you can just spit it. And Kisame spits actual oceans, I think his Suiton skills are much more dangerous than what Tobirama has shown thus far regarding this ability. I still put the Hokage in second place, though.
Mei takes the third place because she is able to douse Madara's Katon, something would require a whole squad otherwise.
The Second Mizukage takes the fourth place due to his hydrification and recyclable explosion jutsu.
The fifth place is either Suigetsu's or Mangetsu's. They don't seem to be too different in that matter.