@TMP Thank you for the response and the advice! I definitely am hoping that campus visits and talking to current students will help. I just got my acceptance/offer from option c this week, so I'm scrambling a little bit to figure out if I'll be able to visit, etc. But I definitely will talk to professors/students in any case.
Good point about cost of living! As far as I know, it is pretty similar in all three places, but I will research more. My impression is that the extra money at option C comes from a fellowship that they use as a recruitment tool. But I also am wrestling over the differing amounts of TAing required at each school. Not having to do any TAing at option B seems pretty significant, and I guess I'm just not sure how much weight to give all the extra time it would allow me to devote to coursework/exams/research. I feel like I'll be able to get a pretty good sense of the people I might be working with, department culture, resources etc. when I visit each school, and I know what it means to live on different amounts of money, but it might be harder to predict the difference that it would make to not have TA duties.
Right now, the fit at option A seems so perfect, but I guess I'm not sure whether I can justify turning down the fellowship offers at B+C... hopefully visiting will lend clarity!