^ Also not just Boston- NYC is an easy train ride, Portland Maine is a nice day/weekend trip, Providence RI is, well, not that great, but it has a lively student scene. And we have ocean and beaches.
I live in Cambridge (between Tufts and Boston), and have family around St. Louis and have visited but have never lived there. I would certainly choose Boston area over St. Louis any day of the week. You will quickly get used to how rude people are here.
And you very well may end up in Cambridge after you graduate:
http://www.livability.com/top-10/college/10-best-cities-for-new-college-grads/2014/ma/cambridge
That said, I really think that cultural fit with the school and student population is more important than location. If you have to pick between these two schools for a visit, I would say that it sounds like Tufts would be a slightly better choice given what you are looking for.