If I had ever seen one in real life, I'd say the Shield. As much as I love Ruger products, the Shield seems to be an all-aces pistol. The only exception is if the LC9 feels significantly better in your hand and points more naturally for you.
I have had a wonderful experience with my LCP and my buddy with an M&P40 has had a great experience with it. You can't really go wrong.
16 Pistols, 5 Rifles, 1 Shotgun, no time to shoot them