The reason I prefer his left side chest over his right is because of his insane shoulder striations and clear visible tricep. His left calf is also bigger than his right, with more vascularity. Then ofcourse his left pec is noticably bigger than his right. Finally, his left bicep peak is much more dominant on the left, along with more vascularity than the right.
There would only be a couple minor reasons to use his right side. He has better striations in his quads from the right, his abdominals also look better on the right, but he's able to cover it up nicely in the side chest. On the right side, his pec detail is better, however it's been coming in from the left side too. Finally, he has good vascularity in his delts from the right side.
But, we are going with the left. Although he's practicing both sides nonetheless.
I'm going to make sure Dave turns back and forth more than other poses during the side chest to make sure every judge can see the back of his arm. That is what makes his left side chest look so thick and conditioned. That is why he doesn't look as thick in this picture as the first shot.