I find that when I carry the Shield in a tilted IWB, the grip hugs my side very tightly and the thinness really helps concealment. The Compact less so. OWB in a paddle holster however, the shorter grip wins, and grip thickness don't make much of a difference.
Neither are range guns, so long session shooting comfort isn't a top concern. Both are large enough for my relatively small hands to be very controllable for quick draw and rapid followup shots. Long slender Shield has a slight edge, compared to stubby 40C... until I swap to a mag with extension, or better yet, FS mag with an adapter sleeve. Ahhh...