Overall, which alliance system was the strongest in World War I? Why?

There were two alliance systems in World War I—the Triple Alliance and the Triple Entente.  The Triple Alliance, formed in 1882, was made up of Germany, Italy, and Austria-Hungary.  The Triple Entente, formed in 1907, was made of France, Russia, and Great Britain.  Both from a military and a loyalty standpoint, the Triple Entente would prove to be more powerful.  Italy left the Triple Alliance in World War I in order to join the Allied powers and to take some land from the Austro-Hungarian Empire.  The Ottoman Empire joined the Triple Alliance in 1914 in order to claim land in southern Russia and to avenge the Russo-Turkish War of 1878.  Germany was the strongest member of the Triple Alliance, and it suffered most of the losses of the Central Powers during World War I.  The Austro-Hungarian Empire was quite weak by 1914, as the different ethnic groups in it were trying to separate and form their own states.
Britain was the largest imperial power in the world in 1914 and had the largest navy—any alliance containing Britain would already be at an economic and military advantage.  France and Russia were great powers in their own right, though Russia would have to leave the war in 1917 due to a revolution.  The greatest strength of the Triple Entente was that Britain and France were able to coordinate attacks along the Western front and that they were able to convince the United States to join the war in 1917.