I don't think I'm anybody's Mucci, but anyway...
Didn't Fraser do his dissertation on just this subject, using FT as his sample? (such a skewed sample in so many ways....)
In answer (from Twickenham to LHR) usually by bus to and then Tube from Hounslow East. If travelling with lots of luggage, a minicab. If its an early start and the client's paying, a pre-booked black cab to (but rarely from; too much trouble finding it and too much expense racked up).
If going to LGW, normally GatEx; minicab if luggage-laden.