Is the current international system best described as multipolar, bipolar, or unipolar?

It was bipolar during the Cold War (US-sphere and Soviet-sphere). It became unipolar for a few years in the 1990s, when only the US remained as a superpower. It is now quickly transitioning into a multipolar system, where there are major power brokers among the US, China, and Russia, as well as European countries through the EU. India and Brazil are also emerging as "poles", though they are not quite there yet.

Unipolar International System

yes, with China's rising as a superpower posing as the biggest challenger to the US hegemonic power. Of course, the results would be more immediate if China and the Soviet Union could join forces to end US hegemon

The leaders could be described as bipolar.

I thought bipolar was an eye problem