Funny thing is that war and hunger are things that always tend to come and go together. War causes hunger, hunger causes war, etc.
By that reasoning, solving World War SHOULD increase food production. Also, if you aggrevate World War by shooting World Hunger, you can unleash a nuclear holocaust that will make the majority of the lands unable to produce healthy food.
There is one thing connecting this thing; population size.
If you shoot World War, population figures will increase so much that food production can't possibly keep up. If you shoot World Hunger, food production should normally go down, but it also causes the population to shrink in size.
Now which one is better;
Birth control is the key. If you shoot World Hunger and unleash devestating wars, there will be less space for humans to live, leaving no means to increase the population until humanity finally dwindles into extinction. Over-populating by shooting World War will only cause both birth and death figures to climb, but there will be no final extinction and the world can eventually try to overcome the obstacle of hunger with the use of technology.
I'm definately shooting World War.