For me, I selected my schools based on location, program fit, and cost (or possibility for funding).
With respect to funding, I didn't want to go into massive debt (more than I already am) to attain a degree for a career that typically doesn't pay well. I already have debt from previous schooling. For others, funding or money may not be as important, so they may focus on other criteria.
With respect to location, I considered the (1) values of the place I would be going to school (i.e. progressive climate or conservative), (2) job prospects upon graduation (e.g. what does the dept. of labor predict for the need for social workers in that particular area), and cost of living (with the assumption that I would stay in the area upon graduation).
Program fit was harder for me to gauge. I am new to this field (it's a career change for me). So I have been reading these boards to get a sense of the different programs and the differences between macro and direct service programs. I'm still not sure where I fall here -- and really could go either way, so long as I am employed at the end of the day. So Instead I have tried to focus on whether the areas of research for the professors match with my areas of interest.