The question would have different answers if it were rephrased:
--What are the best-selling eyepieces in the US aftermarket?
--What are the best-selling eyepieces to telescope makers?
--What are the best selling eyepieces to people who frequent cloudynights.com?
But the original question was:
"Which eyepieces are most popular, not just on CN, but anywhere?"
To which no one has the answer unless all the Chinese companies compare notes (and I doubt they do).
In the UK, a lot of the same eyepieces that sell here sell there, but with different brand names on the outside.
Ditto the EU and Australia. Some Chinese eyepieces are sold under many labels but are the same eyepieces everywhere.
And now many of those Chinese companies are selling direct to consumers through "stores" on line.
So if we were to discover that one of the 8 sellers of a certain eyepiece had the largest sales of the eyepiece, but that, collectively, another eyepiece was a bigger seller (all brands combined),
which would you say is the most popular eyepiece. The one from Barsta, or only one of the 8 labels the eyepiece is sold under?
So there isn't really a good answer to the OP's question. It needs to be rephrased.