Hi from what I have seen diesel wise the best appears to be the 2.8 but these are becoming out of date. the 2.2 seems to be the best on fuel and stronger than the 2.5. the main short coming with the 2.2 appears to be the quality of the fuel injection pumps. If it runs out of fuel quickly seizes if not bled correctly this is in the form of a slight seizure which the rapidly detoriates.
The 2.5 has issues with the head gaskets and general design. [it is still a better engine than the freelander one]
All round i would [and probably will be] buying a 2.2 with some service history and low mileage. The 2.2 is a modern fly by wire type but does not seem to have many electrical problems other than dashboard connection. It does suffer from vacuum pipes splitting on the ends, easy fix but irritating!