My 2 litre 16 valve manual is giving 30mpg on mixed driving,it doesn't get driven hard at all though.
If you go for a 16 valve petrol (they are around half the price of a comparative diesel) check for any nasty noises on idle once the car has warmed up,de-phaser pulleys can give problems and if you can't change it yourself you'll end up with a very nice garage bill.
The 2.2dTi is a bugger for head gaskets and the lack of room under the bonnet with this engine in it can make maintenance.....err.....'interesting'.
If you find a cheap phase 2 car with a 2.2dCi engine then they have a couple of very common (and expensive) faults,I'm sure you'll be able to find them if you have a search around on the forum.
The V6 petrol gives pretty horrific economy but the engine is an absolute peach.....it's just a shame the auto box (V6's are autos only
) that they use on it is pretty troublesome.
Just my thoughts,hopefully someone else will offer their opinions too soon.