Fire- Madara, Sasuke and Itachi can be argued to be betterthough because of amaterasu being able to burn even fire. In overall techniques Madara.
Electricity- 3rd raikage or Sasuke. They both have their feats.
Wind- Danzo, in overalil techniques. Naruto has the most powerful technique regarding wind jutsu, but as far as we have seen he only uses it for his rasen shuriken and splitting a waterfall. He hasn't used any actual wind techniques, but he has the most powerful one. While I think Naruto probably has the ability to be the strongest with wind techniques overall, he has really only focused on putting it into one move and didn't bother to learn any straight up wind release jutsu.
Earth- Madara. He dropped huge meteor out of the sky, Don't even care how he did it. But in all seriousness I would think that the best Earth user would be Hashirama, though we have seen no feats. If you want to call whatever gaara's ability to control sand earth, then maybe him.
Water- kisame or Tobirama