Grain or Bias?

The next step of my toile that I have been telling you about in my recent posts is to add the pin-tucks down the side.  before doing this I had to find out which would be more suitable, on the grain or on the bias?  What I found was the the pin-tuck on the bias (top pin-tuck) has a better shape than the one on the grain (bottom pin-tuck), so this is the one that I will be using.