DTI is better on fuel....I get over 40 to the gallon out of mine if I am nice to it....
The 2.2dti is better on fuel, and is a bit more of a rugged engine, but if the pump goes it will be an expensive fix....and you will probably pay twice as much nearly for one thats done loads more miles than a 2.2i...
The 2.2i is more fragile, but ok if looked after, heavier on fuel, but no pump to worry about and you will pay less buying the car...
You missed out the goodie though...the V6....which is cheap to buy, engine is bomb proof, around the same fuel usage as the 2.2i if you drive it sensibly, sound great, normally better specced and less miles and tonnes of power when you need it...