Only fly in the ointment with Jetstar appearing at MAN is that they seem to be planning on hubbing their flights towards Europe through Singapore. Given that MAN already has a service to Singapore I wouldn't be at all surprised if that moved us down the list.
With regard to the trains - just got back from a long weekend in London, and for the first time in probably 10 years went on the train. Just under 2 hours Stockport-Euston, for less than £90 return for 2 adults and a child, and unless your final destination is nearer LHR (or LGW) than the city centre then it's a no-brainer. Could have got it cheaper but only booked a couple of weeks ahead.