While the receiver could not notice a difference between the three connections, I would say that the caller connecting to a router would still be the most preferable option, as it had noticeably less static.
In January 1994 the then Transport Secretary, John MacGregor, told MPs that Union Railways - the company set up to construct the Channel Tunnel link - had concluded that "St Pancras is preferable to King's Cross as the terminus on environmental, operational and commercial grounds".