ESD potection in the PCB
I usually connect the shield to a chassis ground (not PCB ground) this way any ESD currents are shunted to the case and don't create common mode noise (or voltage spikes) on the PCB and the ESD currents are kept well away from any electronics.

I have also had issues with external cables and their connection to the chassis. The best place for the ESD spike current to return to (if the voltage is applied on the shield of the cable) is to the chassis. I have had issues if the shield of the entry cable was not tied well enough to the metal chassis of the instrument. Once we tied the chassis to the USB shield the currents returned through the chassis and stopped causing a failure of the test. 



I think the general idea is to shunt the current away from the PCB before it ever becomes a problem (with a chassis ground (through a fastener) on the PCB separate from the PCB ground), if your design does not permit this, sometimes the way to go to slow ESD spike down and create some impedance to reduce noise is by a resistor as shown above. ESD testing can be tricky and it really depends on the entire product, the best way to test is to have some options to see what works, because I've had designs that work well in one product and do not work well in another. Make sure you also have an ESD filter on your data lines also (which you may have but don't show)