Yes, but one army did not have an edge over the entire century. A century, at that time, was nearly three generations. And militaries of the time could only serve for a small timeframe, so you could have up to ten different generations in one army for this century.
During the 18th century, in Europe, armies were in a very subtle situation. Different factors led them to be of quality and efficiency. I will concentrate on Western Europe since there has been a variety of situation in the East of Europe (East of Prussia), and the South (South of Austrian Empire).
Some of the factors were as follow:
- More training and skill management
In Europe, after state built themselves during the end of the Middle Age, they had started to fight for a variety of reasons. But the main point is they moved from the mercenaries of 16th century into government's armies. This led them to manage skills of their soldiers: training included drill, tactics were written, and officers slowly started, during the 18th century, to attend to military schools.
During those centuries, and especially during 18th century, musketry, rifles, and artillery had major technical evolution. This came from the actual manufacturing of the weapon to better logistics and new tactical possibility with faster loading and firing (especially for artillery). I am not aware of technical evolution for cavalry, but the development of lighter firing weapons led to mounted rifles and dragoons.
All of these evolutions needed to be appropriate by soldiers, and some were only during Napoleonic Era. But the point is that different countries had different innovations at different time, so the resulting quality of their armies was varying fast.
By the way, this has been also true for navies, but I won't speak of that there.
- Officers changed. Kings changed
Remember: this was not a time for meritocracy, there was still a lot of noble people who managed to get into military responsibilities for who they were born, and not for what they were able to do. But failure is a failure, and sometimes king and ministries changed their mind and dismissed commanders. This is not to say that officers were always stupid men, some of them were truly capable. But this is to say that the quality of commanders could change fast, at top as well as lower commanding scales. As a result, the quality of a given unit could change and could be more or less well used by high command.
At the time of the 18th century, centuries of war in Europe had built social identities. John Keegan quoted some of the "military people" of Europe in his Battle of Normandy. For example:
- Different Germanic people such as the Hessians
- Prussia, as it developed a fairly big army compared to the size of the state
Those people ususally provided units to larger countries, as mercenaries or as regulars, such as United Kingdom, Austria, Russia, and this resulted in different quality in one country's army.