Not sure which driver to install? This may help.
The VISA standard is a relatively low level driver standard designed to provide a common style of interface to devices, the basic commands to access a card are pretty standard for any product. However when it comes to control, each device may have dedicated commands.
The IVI standard aims to standardize the control functionality too, and IVI have published individual specifications for different device classes; our driver conforms to the Swtch class. This standardization allows more interchangability than other drivers, so long as the user confines drivers usage to the standard functions. This interchangability then leads to the possibility of standardization for the software vendors. The primary use of our IVI-C driver is in National Instruments Switch Executive, which allows a degree of abstraction from the driver and card details.
The choice is yours, Direct IO driver, VISA driver or IVI driver. Which you select is more driven by programming environment than any thing else. If you are using Switch Executive, then the IVI driver is the choice; if you are using a VISA environment then the VISA driver is the choice. If you don't have VISA then the Direct IO driver is the way to go.