I have a mk6 1.4 turbo on a 10 plate which returns 35mpg round town going to school. I couldn't justify the premium of a tdi or the potential horrendous engine repair bills if it were to go wrong just for an extra 15mpg.
I also do sod all miles which also helped when buying the petrol version.
Agree with the petrol vs diesel but I do over 20k.