@display name, thank you for your advice on advisors. I think I am fortunate in that my potential advisors at both institutions have been spoken very highly of by their present students, both those starting their degrees and those on the threshold of completion. That being said, the placement rate of the POI at university A not only matches but possibly even exceeds the department's already impressive baseline: his students have not only generally performed well, so far as I can see, but have even at times landed positions at top ten institutions.
There is also something of a development: I have finally gotten to speak to one of the professors at my home institution, the sort of grizzled academic veteran who at this point seems to know everything about the field and everyone in it. Considering the differences in prestige and placement rate, and his high opinion of the POI's work, he advised going to department A if it was at all functional—toward which end he helpfully offered to email the relevant faculty, as he knows them decently well, and see if he can figure out what is going on. So I hope to have some more definite answers soon.
Also, I should have made clear earlier that I am first on the wait list of school A rather than admitted; school B, by contrast, is my top choice of the ones I have thus far been admitted to. I posted the topic now, however, because if the wait list response comes on the fifteenth itself, as seems possible, I would like to already know how I want to respond. Your suggestion of a Skype meeting, @fuzzylogician, is a good one, but one that I am hesitant to do unless admitted. Though I suppose that, between my own email and now my professor's, I have been taking up a fair bit of the POI's time already and should perhaps just go for it. I have actually met the fellow once before, though, when he gave a talk at my school. We got along well then.