It is very hard to generalize about the political systems of each of these times because there were great differences between the systems of various states in each of these times.
What one might say is that the political systems of the Renaissance were less extreme and were generally in smaller states. There were more differences between Enlightenment-era systems and the systems existed in larger states.
For example, in the Renaissance there were both autocracies and republics just within what is now Italy. However, there were not huge differences as in later times. There were not any constitutional monarchies with really strong checks on royal power. At the same time, there were not absolutist monarchies either. Many countries were still split up into small states or into feudal domains whose lords had a great deal of power.
By the time of the Enlightenment, things were more extreme. There were solidly constitutional states like England with strict limits on royal power. At the same time, there were absolutist states like France. Feudalism had largely died out and, outside of Germany, states were large.