Neither Athens nor Sparta can be characterized as an oligarchy in the traditional sense, but they do exhibit different forms of governance that have elements of oligarchic rule.
Athens is known for developing democracy, particularly in the 5th century BCE, where citizens participated directly in decision-making. However, it is important to note that this democracy was limited to free male citizens, and the lower classes and women were excluded, which could suggest an oligarchic aspect depending on how one defines the term.
Sparta, on the other hand, had a mixed government system that included elements of oligarchy. It was ruled by two hereditary kings and had a council of elders (Gerousia) and an assembly, but the real power remained with a small group of elite citizens.
In summary, if you are looking for a system more closely aligned with oligarchy, Sparta is the better example. Therefore, the most accurate response would be Sparta.