Pitt stat and biostat were both ranked in the 2014 US News Rankings. And Pitt biostat was 0.1 point above the stat department. It's strange that Pitt biostat is not even listed in the new US Rankings. Maybe the recent change of department head is the reason.
I think the location of the university matters, too. Large cities tend to offer better job opportunities.
As for the biostatistics program rankings, UMich ranked fourth and UT SPH ranked seventeenth according to the post here. The Department of Biostatistics at Vanderbilt University is not ranked, perhaps because their program is relatively new.