ClearSCADA is able to read and/or write to data on other servers using one of two OPC standards: OPC DA, and OPC XML-DA. Whether you choose to use the ClearSCADA Advanced OPC Driver, the ClearSCADA Guide to the Simple OPC Driver, or the ClearSCADA OPC XML-DA Driver, depends to some extent on your system setup.
OPC DA is more efficient in terms of network bandwidth than OPC XML-DA. However, OPC DA is based on DCOM and can be problematic to set up when the driver and target OPC DA server are on opposite sides of a firewall. OPC XML-DA uses standard web protocol and is much more firewall friendly. If network bandwidth is important, use the ClearSCADA Advanced OPC Driver, or the ClearSCADA Simple OPC Driver, to communicate using OPC DA; if easy setup is important, use the ClearSCADAOPC XML-DA Driver to communicate using OPC XML-DA.
The ClearSCADA Advanced OPC driver provides additional functionality to the ClearSCADA Simple OPC driver, such as support for redundant OPC servers. If both the Advanced and Simple OPC drivers provide the required functionality, consider using the Advanced OPC driver rather than the Simple OPC driver. Using the Advanced OPC driver will give you more flexibility should your system requirements change in the future.
For information on the other OPC drivers, see the ClearSCADA Guide to the Simple OPC Driver, and the ClearSCADA Guide to the OPC XML-DA Client Driver respectively