I agree with the responses above that Germany suffered the greatest consequences from World War I. Germany is sometimes blamed for the start of the war and for that reason the price at the end of the war was the most burdensome. The Treaty of Versailles claimed much of German territory to be turned into the possession of the surrounding countries. It was also given a great amount of fine which lead to the collapse of German economy and huge inflation in the market. Such results contributed to the rise of Nazi regime and could be considered long term causes for future actions taken by Germany.
I have to agree that Germany suffered the most from WWI. Regardless of their agression the poverty and prejudice that resulted from WWI created an ideal situation for the rise of the Nazi party. People who are starving and suffering will respond to promises (and results) that alleviate these issues. People who are hated will cling to an opportunity for national pride. I think Germany suffered the most because the long term effects of WWI were greatest in Germany. Everything that happened in Germany until German re-unification was in some way a result of WWI and the Treaty of Versailles.
I'll go with Germany. It is true that the war was not fought on their soil, but the impact of the war on their country was more lasting. The Treaty of Versailles punished them in a way that was disproportionate to their culpability for the war. They had parts of their territory taken away from them and they had to pay reparations that devastated their economy.
The top two countries hardest hit were Russia and France. They both had devastating military losses, economic hardship, and decreased morale after World War I. Russia had the most casualties in the war (roughly 3-3.7 million total deaths, including civilian estimates), which, considering their early withdrawal in 1917, makes that number even more severe. Based on casualties, Russia suffersed the most as a result of World War I.
World War I puts too much strain on Russia at the least possible opportune time. With the extra pressure on the economy and the growing dissatisfaction among the poor, Russia is ripe for revolution and the Bolsheviks seize power. Russia will no longer be the same--literally--because after that, the country known as Russia ceases to exit. The USSR is born.