I’ve owned both at the same time, the Ruger felt smaller and was almost small enough to pocket carry. I think it’s about 2 oz lighter too.

But I sold the LC9s and kept the Shield, the Ruger trigger shape would blister the side of my finger unless I just used my fingertip, and the Shield shot much tighter for me due to the shorter travel of the trigger and lighter recoil.
The ruger grip feels much thinner, it feels like the center of the grip is thinner than the front & back. The Shield grip just fit my hand better.

I have several Rugers, some old, some new, all great. But I had several small issues with the LC9s and when the front sight came loose after 300 rounds I lost confidance in it. No doubt Ruger would have made it right, but the Shield just shot better and after 4 years has not had one issue or failure with any ammo.