I couldn't find much info about the Connection State parameter: I checked a couple of my elements and it seems to have 'Undefined' for all connections. However if the parameter is working fine for you, you could follow this logic:

Communication State comes from a table that show information for each connection individually so I would say it could be better to use if you have multiple connections.

Next to that, the element usually has a fixed time before it goes into Timeout. If this is not the case for the Connection State, that could be another reason to go with that parameter instead.