I don't know how to rate BA in terms of other cities in SA, but I wouldn't think it's too different in any way, really. I don't know if I'd say it's the safest - I actually feel much safer in Asuncion in Paraguay (though it's not nearly as big, a fraction of the size) but I know people who don't agree with me on that one. I know both cities fairly well, though.
Thing is, unless you are going to "1st world" countries you probably won't get any better. And even in those "1st world" countries, in big cities, you can have the same sorts of problems. I just don't think it's quite as likely there as here, but others disagree with on that as well.
Come on down. You'll be fine.