The answer depends on what information you are wanting to get out of the meter. If you are looking for historical information store in the onboard logs, ION is the protocol to get this information. If you are looking for information about that last sag/swell, then you can customize both IEC61850 or Modbus to give you that data. Note that IEC61850 is limited to just 16 additional analog measurements, modbus has a much larger number of registers available.
If you are looking for more than just the last PQ event you could possible use store modules to keep some history, depending on what information you want to store and how many events back will determine the number of store modules needed.