That's a very good question.
I think, as you pointed out, part of the justification for splitting the two is for accountability purposes: to know how much money is going for post-secondary, how much is going through the Canada social transfer.
One of the advantages of the dollar-for-dollar or the matching funding, which addressed the issue of paying in proportion to need, was that it gave a clear accounting for how much money is spent on social welfare issues. The other benefit of going that approach is that it actually helped to encourage the development of Canada's social system.
Can I say definitively what's the best? No, I can't. But I think these are the kinds of questions that we need to be talking about when we talk about splitting up the Canada social transfer: how do we make sure it works to actually deliver to the needs across Canada to improve well-being and assure there are adequate social services?