Seems to me it would be nearly impossible to determine the "biggest selling" host. The time span is huge so the value of a dollar varies, and you'd have to know how many hours each host was on air, which air times/ products were "easier" for selling, are you comparing number of units sold or dollar amounts, etc. From the snippets I've seen on social media, Kathy and Lisa are friends so they might not like the idea of comparison. I've read that Coleen Lopez is a top seller, too, by the way.
Few things reveal your intellect and your generosity of spirit—the parallel powers of your heart and mind—better than how you give feedback.~Maria Popova