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.
Beretta PX4; 92FS; 92S; 8040G | Sig Sauer SP2022; P6 | Colt Python 4"; 1968 Detective Special 2"| Smith & Wesson M642 No-Lock | Ruger LCP; 10/22 | Daniel Defense M4V1 | Remington 870 | Alpine M1 Carbine | Steyr M1895 |1943 Izhevsk Mosin M91/30 | Walther PPS