When did you apply? Depends on why did u apply, scholarship, etc? BU better ranked, their functional and context certificates seems more practical. Tufts for hospital work, research, continue education (MD). Both good program if you cant decide and need more time, pay your deposit / ask for more time.
It is a little concerning that BU wants you to reply in a week, BU might go all online in fall, and that's a bigger problem at BU than other schools as BU leaves much to be desired when it comes to just being amicable with students and making the whole process easier if possible, in general they don't really care that you "chose BU" or that you're trying to get an education to make the world a better place, it's the Dunder Mifflin of graduate education. If you're left with online Zoom classes, (I'm sure a nice picture of BU in the background) and not a lot of opportunities in Boston, you might as well take the same classes online anywhere else and save yourself the administrative red tape at BU.
There was a group of BU students this summer that paid around $30,000 to do an accelerated six week course in London, and it got cancelled, and all they got was some classes on Zoom, but were still required to pay the full tuition after apparently being told they wouldn't have to, there are going to be lawsuits and there already are for unrelated issues regrading charging students for meal plans rendered worthless by coronavirus, a low blow and it took calling them out on the media for it to change. Doubtlessly the faculty and higher administrative types at BU like going to conferences and living in Boston, but there's just apathy when it comes to the students.
Tufts students are MUCH more relaxed and at least that school has a phenomenal nutrition program, something you can be proud to be affiliated with. For the tuition BU charges their curriculum is really bad, though they want to fix it.
Based on comparing where Tufts grads go vs. BU a couple years ago I concluded that Tufts grads do a slight bit better in the job market.