Most Common Coin Ever Produced?

The answer to your question is not as easy to research as it ought to be, partly because the world's two most populous countries, India and China, don't have published mintage figures for recent circulation coinage, not in the Krause catalogue, anyway.

There are, however, some old Chinese coins that I know could easily give any American coin a run for its money in terms of quantity issued, because these coins don't bear dates and were struck over a very long time. The "Kai Yuan tong bao" cash coin of Tang Dynasty China was struck with identical design for nearly 300 years, from AD 621 to 907, at a time when the Empire was rich and prosperous. While the total mintage of this coin type is incalculable, there were easily billions of them produced; some years for which the mintage records have survived give numbers in the millions of strings (a "string" being 1,000 coins).

Likewise the coins of the reign of the two longest-lived monarchs of the Qing Dynasty: the Kang Xi (AD 1661-1722) and Qian Long (AD 1736-1796) emperors both reigned for 60 years and were likewise peaceful and prosperous times. Coinage issue was somewhat more centralized under Qian Long; the "Qian Long tong bao Revenue Mint" cash coin is probably the coin with the highest mintage of any coin, anywhere. Even today, over 200 years after they were issued, they are still so common they are only worth a few cents each.

It's a bit liking to ask
" What is the fastest car?"
The question needs exact definition.
However, I doubt if you get a better answer than Sap's.

1 out of every 4 nickels I get is a 1964 and after looking through tons it'll drive you crazy!

Weren't these minted in both zinc and bronze--is there a breakdown for that? I imagine the bronze one will eventually get taken out of circulation.

Now you're being pragmatic--which is sorely needed in our currency program!

Here is something to wonder about. Some day in the far, far future when all of this is gone and only ruins are found by people from other planets, which item will they find the most of. A Twinkie or a 1964 Nickel?

The 1964 Nickel.

I have already eaten through my hoard of Twinkies.