But I can't fit a shotgun in my pants
Mathematically the XDS at 5 shots gives you 0.802sqin surface area entry wound. The Shield at 7 shots gives you 0.693sqin surface area entry wound. Therefore, the XDS, if all shots are on target, leaves a bigger hole.
My preference? 9mm Shield IWB for EDC and XDS Pocket Carry for if the BG happens to be drugged up and won't go down. I own the Shield and I want the XDS. For some reason I keep buying Beretta Mini Cougars instead so take my advice for what its worth.