train v coach
my vote goes with the train.
having crewed from LGW in the past done the Cardiff to LGW journey rather alot. Just go straight through to Reading and change, try to plan your journey so you'll get the service from Reading that doesn't stop so much.
As previous post says you can get some cheap fares. If your travelling on a weekend you can get a weekend first upgrade for £8.00 one way on the Great western bit of the journey. Well worth it to rest those worn pins in style after a long busy flight if you are crewing
There have been occasions when there have been problems just give yourself an extra hour for the journey
The Coach is now a little bit of drag does go everwhere as post Sept 11 services merged etc. There used to be a coach straight through to LHR central bus station then down to LGW but no longer that simple.