Choosing Grad School?

When deciding on a Grad school is it better to consider the overall ranking of an institution or on the ranking of the faculty itself?

I ask this because I live down under (Australia) and some universities rank fairly well in terms of Computer Science faculties, and similar areas, (namely ANU and Melbourne) but they don't do as well in overall rankings in comparison to some US options (which could be costly to do through international programs).

Thanks.

Note: For masters.