[My logic:
The "crown jewel" is not merely something we like, or even the most popular game show that the network aired in the period, but the one most important for the genre of the daytime game show on the network in question.
I will go in order from easiest answer to hardest:
CBS: The Price Is Right, for all the obvious reasons.
ABC: The Dating Game. ABC as a major figure in the genre post-1965 has its roots in that program's success. The other candidates for the post have issues: Family Feud, while a big hit, seems to have been in a vacuum (note that nothing followed it), Deal and Pyramid were both pick-ups from other networks (and don't feel right for this concept), and there aren't any other real candidates.
NBC: NBC is complicated in this consideration for two reasons. One of these was the fact that it didn't have the lulls that the other two networks had in the 1960s, meaning that its holdovers, while obviously important (Concentration, Hollywood Squares, and Jeopardy! did run for forty years combined, after all), can't be pointed to in quite the same way that the other candidates can be. The other is that, of the game shows that premiered after 1970, NBC had a tendency to produce a great deal of hits that seem a notch below "crown jewel" (and, yes, I'm counting network Wheel). I'll pick Hollywood Squares for now, and admit that this is very liable to change.