Dunn seems to be a guess hitter so this makes since.
I think the term guess hitter is an over-used term. All batters are anticipating or "guessing" certain pitches and locations in given situations. Unless the batter is a total nitwit, how could they help not guess/anticipate?
The count is obviously important. Certainly there are favorable fastball counts
. If Dunn has a pitcher in a hitter's/fastball count, he is most certainly looking for a fastball to drive. That is what he is paid to do. Now, if he is in a hole, he is not looking fastball because the pitcher is going to be trying to get him out with sliders/breaking balls off the corners.
There are other factors that dictate what Dunn or any batter are looking for such as runners on base, score, inning, as well as pitcher's/batter's history.