I like the look of the Liberty and have checked them out on a few occasions, but their fuel economy in relation to their size is not good. The gas fours are rare, and don't really offer much better economy anyway. The CRD's do well, but are rare and expensive used.
It also seems that a good many of them were sold with the true part-time 4WD and not the more versatile unit that allows an AWD usage, which I greatly prefer in the city.
However, for real off-roading, the Jeeps are near the top in capability, so if you really need it, it would seem to be a good choice. The Grand Cherokee is awful in terms of build quality, so the Liberty looks like the one to find if you want a Jeep with four real seats.