I have to go with Iran. I mean you look at what has been on recently as far as Iran threatening the US to keep their air craft carrier away from global waters is just a begining. However I think it is a bluff. The US said they wouldnt allow Iran to block any waterways or tell them not to do routine passbys. I don't see Iran making a war out of that. I think the reason they end up going to war is over nuclear weapons. Iran says it is for energy... well I doubt that. The US stated they won't allow nuclear weapons in Iran and would have to go defend Isreal. And would do whatever they had to do to get them out.
I also think they go to war 3-6 years from now.