Always use the camera's "native ISO" whenever possible as it is what the sensor records at by default. Every other ISO is either an amplification or attenuation of the original and has the potential to introduce noise and artifacts. The reason lower ISOs are there is for situations where native ISO will not allow you to achieve an exposure parameter that you need. For example, you want a 3 second water exposure and at ISO 100 and F22 you can only get 1 second, even with the 2 stop ND you brought along, so you choose one of the Lo settings allowing you to shoot without over-exposing and losing details (at the cost of potential noise).