Time: January 18 to 21 (event already took place)
Location: The United States (White House)
This was one of those high impact but low probability events.
When Richard Nixon visited Chinese Chairman Mao Zedong in 1972, it paved the way for the rise of China and the enjoyment of cheap goods by Americans. This visit was easily one of the largest economic events in the last three decades of the 20th century.
Now, as China becomes the second largest economy of the world and continues to run persistent trade surpluses with the U.S., the two countries are at a crossroads again.
The key question is if China is ready to become a nation of consumers. To do that, it needs to make big decisions like providing more generous social safety nets and cutting back subsidies to exporters. Allowing the faster appreciation of the yuan, combined with other sensible reforms, is key to addressing both issues.
The U.S., on the other hand, needs to consume less and invest/produce more.
If China and the U.S. actually agreed to adjust their distorted economies for the benefit of themselves and the world, it would have been one of the biggest economic event of the 2010s decade.
However, Hu's visit to Obama ranks 5th on this list because nothing likely happened. For both sides, there was too much political inertia to make any real changes. Plus, the visit -- which already ended -- did not produce any publicized concrete results.
Still, even if a little progress was actually made behind the doors -- for example, if China agreed to appreciate the yuan slightly faster -- the impact would be noticeable given the sheer size of these two economies.