Who was a better ruler and why: Peter the Great or Louis XIV?

It all depends on how you define what makes a good ruler. Certainly, both men transformed their respective countries, for good and ill. Under Louis XIV, for example, France became the foremost military power in Europe. There wasn't a single conflict during Louis's lifetime that France wasn't somehow involved with, either directly or indirectly. The downside of France's growing military involvement in the affairs of Europe was that it was ruinously expensive.

Nonetheless, by the time of Louis's death France was the undisputed power in mainland Europe, having significantly expanded both its borders and its influence. In the present day we tend not to look too kindly on territorial expansion achieved by military means. But during Louis's reign it was widely regarded as a sign of true greatness. By the standards of the time, Louis XIV was unmistakably a great ruler.

One must also recognize the immense cultural primacy that France enjoyed during Louis's long, tumultuous reign. France became the undisputed arbiter of cultural taste in Europe, a position of supremacy it was to retain, in one shape or form, for centuries. Under Louis there was a flowering of the arts the likes of which had never been seen before in France: the dramas of Corneille and Molière; the music of Lully; the sumptuous Baroque splendor of the architecture of Le Vau. The great cultural achievements of France were feted throughout the civilized world. 

Peter The Great, like Louis, was a ruthless autocrat who utterly transformed his country. But military greatness and territorial expansion were just parts of a much bigger story. Peter had a vision: he wanted to change Russia. At the time of his accession, Russia was widely perceived to be hopelessly backward—a second-rate power mired in ignorance, superstition, and obscurantism. So Peter set about dragging Russia, kicking and screaming, into the modern world. From now on, Russia would be more European, less Asiatic. It would get rid of the old ways and embrace the very latest developments in science, technology and military tactics.

As with Louis, Peter greatly centralized the state, crushing any last vestige of opposition to his unbending autocracy. But this policy, like the blatant imitation of European ways, was simply a means to an end. And that end was the strengthening of Russia's military, in the process turning this vast, unruly land into a major player in European power politics.

Peter presided over the building of the first Russian navy. This helped Russia to achieve a number of notable military victories including the capture of the Ottoman city of Azov in 1695. It also checked the growth of the Swedish Empire in the Great Northern War while at the same time expanding Russia's frontiers.