Best location has to be NWest of London, off the proposed HS line and near the M40.
It always amused me with Boris Island that no thought was given to this with the line stopping well short of the airport...you could not make it up !
Same with the STN option although that is now dead in the water.
The Davies commission kept harping on about a UK hub but seems to have completely forgotten about its remit.
In my view somewhere near White Waltham ?
Still commutable for Heathrow workers...!
Far enough away from London so no need to overfly
Close to M40 / A404M for Midlands
Next to M4 for West
Close enough to HS for short branch line re NWest
If its an airport for the UK make it, "for the UK" not just London !