I feel like each of these weapons is a fine choice (though I am admittedly less knowledgeable about the Nano), but each has drawbacks. For me, It would come down to evaluation of each one's shortcomings and which would affect my comfort with and use of the gun.
They're all pretty tiny, which is good for carry, but also means there isn't much space for my fingers to hold them. Here, I would say the LC9 gives me the most comfortable and confident handling. The Beretta (the only one of the three I haven't handled), seems to fall in last place there. I don't know if there are extended grip mags for the Nano, but i think there are for the Shield, so this point may be moot.
I'm not a fan of the M&P triggers. That hinged design feels like it's going to break off. But it does engage fairly quickly, unlike the Ruger, which has a solid trigger, but its "DAO" (not really DAO) action leaves you with a long, empty pull before you fire the round. The Nano trigger LOOKS like a Glock or XD trigger, and if it feels the same, my vote goes there.
The bulk and roundness of the M&P seems to be the design least conducive to concealed carry, while the LC9 is probably thinner than my cell phone with extended battery (seriously, that thing is CONCEALABLE).
Lastly, there is absolutely nothing on the Beretta that can snag - no slide release, no external safety, no grippy surface material - nothing. That's worth some points to me.
Jeeze. Who knows? it'd be tough to pass judgement without feeling the Nano, because I get the impression it might be my choice with an extended grip mag. Until I can say for sure, I think the LC9 would edge the M&P for me when I come down to its main intended function, which is very light, concealed carry in just about all conditions (though the M&Ps are great guns overall).
I hope that didn't make the decision even more difficult. The best thing is to handle them all.
