I agree Friedrich Nietzsche is the most influential philosopher of the 19th century. He covered such a wide range of topics with all of his writings that it is just impossible to even compare him to anyone else. His ideas on religion and the meaning of life have changed the way Westerners view philosophy forever.
I hate to say it, and many people may not like to hear it, but Karl Marx was the most influential philosopher of the 19th century. Marx's ideals, in one way or another, influenced a huge portion of the world's governments in the 20th century, even up until governments today.
Karl Marx is more influential in the fact that his theories caused revolutions in the 20th Century. Marxist thought penetrated Russian society and caused two world wars and several regional conflicts. Millions of people died because of Communism and Marxism. Marx was by far the more influential philosopher because no one died because of Friedrich Nietzsche.
Throughout the 19th century there were many other philosophers who did more and discovered more that Friedrich Nietzche did. Although he was a great man, and was very gifted and smart, he was not the greatest. This German did do a lot for his culture through his works and ideas though.
No, I do not think that Friedrich Nietzche was the most influential philosopher of the 19th century, because there were so many that came along during that time period that it was hard to choose one to be the most influential. They all have influences that come from each other. There were also some great philosophers in the 18th and 19th centuries in France that really influenced the American revolution and its aftermath. Nietzche was only one of many greats.