Well, they both consistently rank in the top 25, so that may be a draw. I will say that BC ranks higher (pretty much without fail) and as a university in general outranks BU in a major way.
While undergrad rankings are pointless to this conversation in terms of programs, it can be important later in life. BC is a top 35 national university while BU is closer to 300-400. Perceived rank and prestige does matter in my view.
That said, feel and fit probably matter more, IMHO.
In that regard, there's not much similar about the two schools (I've taken classes at both).
BU is urban. BC is very suburban. At BU everyone is anonymous and everyone is a number. At BC NO ONE is anonymous. At BU you will constantly see faces you don't recognize. At BC it doesn't take long until you seemingly know everyone you see around campus.
BC feels very much like family. BU feels very much open and flowing. BC is a slow to react and a bit old-world. BU is 10,000mph and modern.
Go to both, walk around, see what feels right.