I'm guessing that these dominate all others by quite a margin, the ubiquitous Victorinox Classic (known mundanely as the Swiss Army knife).
This. ^
It's been a few years, but Knife World magazine did an article on Victorinox. In it, one of the Victorinox people being interviewed gave the following figures. They make 35 million SAK's per year. Of that, 9 million of them are the humble classic. 9 million classics every year. By comparison, Buck made an announcement a few years back, that since 1963, when the model 110 was introduced, theyhad sold 10 million of them. It took them over 40 years to sell as many Buck folding hunters as Victorinox sells the little classic every year.
Victorinox also has the most modernized knife factory in the world, and Opinel is second.