1. Public financing. This is the most successful; even if there's a reputation of bureaucracy and mediocrity (largely because public schools have to contend with the full range of inputs) the system actually works extremely well. A lot of people (read: short-sighted conservatives) just don't want to pay for it, so they gripe about the public-school model itself, rather than (admittedly, serious) issues with execution.
2. After-the-fact donations. The problem here is that it converges on a Nash equilibrium where the rich get the resources anyway because they are most likely to be future donors. (Depressing news: in spite of the "economic miracle" that college is supposed to work, but hasn't for a long time, the #1 predictor of whether someone will be wealthy is having wealthy parents.)
3. Non-dischargeable debt. Student debt might have been a good idea (a) before it started having effects itself on pricing --making college again unaffordable and replacing minor debt loads with indentured servitude-- and (b) were the economy less volatile than it has been since 1990 or so. It's horrible now.
None of these solutions (of the three, public financing being the only one that works) admit themselves well to the startup business model.