"they both like Vingt-un better than Commerce"
Creative Commons AttributionBlackjack - Credit: banspy, Flickr

Vingt-un or Vingt-et-un is the French version of what became Blackjack, with a few alterations. Vingt-et-un, French for twenty-one, originated at the beginning of the 18th century in French casinos.

Commerce, on the other hand, was invented a century later, also in France. It is similar to Vingt-un, so the comment regarding which Jane and Mister Bingley both like best shows how little they know one another yet. This is, of course, the point of the comment made by Elizabeth.