I don't think we can know what the most popular until both are freely available in the retail environment. Retail stores are selling every iPad Apple ships them. So Apple is determining what is most popular by choosing which colors/models they have shipped. Probably the one real gauge would be if Apple released what the top models selling through the online Apple Store, where people are willing to wait for the exact model and color they want.
I wanted black 64gb WiFi, but got white 64gb WiFi because that is what was available at the store.
I wanted black 64gb WiFi, but got white 64gb WiFi because that is what was available at the store.