I think Dave's perceptions of Heidi and Christy were greatly influenced by everything Jenna said. Jenna, of course, talked up Heidi as being a wonderful person and strong team member so he thinks she is a greater asset than Christy.
Butch and Roger, on the other hand, are forming their perceptions of Heidi and Christy based on direct observation, and I think they are seeing Christy as a greater asset.
Which she is, as a TEAM member. They may change their minds once the teams merge and competitions are for individual immunity and rewards!