If you are considering any of these pistols, you should also consider the Kahr CM9 (or pricier PM9).
It's a bit smaller and easier to conceal than the Shield, and just as easy to shoot well.
The CM9 is a huge step above the LC9 in my experience. It's easier to shoot and softer shooting, is simpler to use and maintain, and has a MUCH better trigger feel.
I can't really compare to the Nano, since I haven't fired one.