If you're sure about wanting to run the progressive Catholic school, I would choose BC. Not only will you be going to a Catholic school, but you'll also get some connections to many more Catholic educators in the US than you would at Vanderbilt.
Speaking for Vanderbilt, Nashville is definitely a city (but not a "big" one), and the professors have a fairly good age range mix (with a few more less-than-60 professors than other ed schools I've visited). That said, Nashville doesn't compare to Boston; if you have any particular questions about living in Nashville, feel free to PM me.