A little ironic for me this subject - as an "ex-pat" Mancunian, who used to live near to MAN Airport and therefore commence many a rail-journey from there to York / Newcastle-Tyne on many occasion , I now live between Hitchin & Flitwick:
I flew ex Stansted last year and traveled by rail , Hitchin - Cambridge - Stansted , and return. The rail journey was pleasant enough and knowing in advance it was going to take well over an hour was no issue and far better than using the car and having to pay parking......
Service was fine but I did find it strange that the EMU's at Cambridge marked "Stansted Express" were going to Liverpool Street NOT via Stansted , and that our eventual train was the XC from Birmingham to Stansted - so, although it worked for me, I'd have thought more EMU's ex Cambridge could have gone via Stansted......
Next month we have a flight to catch ex Gatwick , so we're on the service ex Flitwick to Gatwick ( Thameslink ) - it will be interesting to see how that works for us...again , far better than an "M25 rat race" me thinks.....
I suppose a lot is the luck of the draw as to whether you're near to a railway station and that railway station is linked conveniently to the airport your wish to use.......
apologies if I've made you all yawn..........