Actually, if you take corn cobs into consideration,
No offense intended to anyone, but I would rather not. You see, if you include corn cobs and other cheap mass-production pipes like Medico or Grabow, you will get an entirely different result than you would serious artisan pipes. Not sure what any of this proves, but since the USA has the "corn belt" and is (I think) the largest producer of corn, then it only stands to reason that we would make more (all?) of the corn cob pipes.
But when you consider the size of the USA to most other countries, then add in cobs and cheap production pipes made easy by American industry, then what other country even has a chance? And if all the weighting is slanted toward only one outcome then does the poll really have any true meaning.
So I think it more meaningful to talk about /length or duration/ of production, and of serious artisan pipes, pipes which are difficult and time-consuming to make. And maybe pipe production as a function of population. When I look at it that way, the first name that comes to my mind are the Danes, followed by the Europeans, around the Mediterranean of which most of your quality briar comes, followed by Turkey and its Meerschaum.
Some of these smaller counties have invented and maintained the fine tradition of very high quality pipe production for many centuries without which there might not even be a pipe industry today.
As with most things, you can get a very different answer to any polling depending on how you want to weight it, and to me, it carries much more weight the /quality/ of the pipes you made and for how long, rather than just bulk numbers.