If you live on the C line live as close as possible to Cleveland circle which is hte end of the line. From there it is only a five min walk to the B line which will have you out to the main campus where you catch the shuttle in ten min. Or you could live at chestnut hill on the B line where it is only a 5 min walk to the C line for getting downtown.
The problem with the B line inbound is that there are stops every 10 metres. The C line has half the stops and so is quicker for getting downtown.
best place to find apartments/roommates is either thru BC or craigslist.org.