Type-s brings up a great point, you can't know and the basic premise is that it's very hard to compare schools. Certainly some schools are probably more difficult academically than others (the schools integrated with the med schools come to mind) and others are probably more rigorous clinically.
But the thing I really wanted to comment on is this "myth" that so called "clinical" schools and so called "research" schools exist. With the exception of Harvard, which if I remember correctly has a research requirement for graduation, "research" schools simply don't exist. Therefore every school would then be classified as "clinical". The thing that many are confusing is that the schools many assume to be "research" only offer more research opportunities than other schools. Michigan, where I go, is a major research institution. This is a University-wide phenomenon. Other schools aren't research institutions and therefore it is expected that their dental schools wouldn't follow suit. We don't have any research requirement for graduation, we have lots of opportunities to do research if that is your thing. For many it's not so the research component of the school doesn't matter.
Continuting this thought, there is a perception that by going to a "research" school you will better prepared to apply to a clinical specialty. Many also cynically comment that this is also because grads of "research" schools aren't clinically competent to be general dentists. And somehow by default the opposites are true of grads of "clinical" schools. These are all completely false. The ability of one to be an outstanding general dentist or applicant for a clinical specialty is completely dependent on that individual. Sure certian facets of certain schools might help you either way, but not enough to make an overwhelming difference. The greatest determining factor is you. And quite frankly, no matter where you graduate from, your first few years out you will suck. Period. Sure there's different degrees of suckiness but compared to the clinician you'll be 5-10 years after graduation, you'll suck right out of school.
