I am going to say what I've always said about this question and say that the best premed program for you is the one that will maximize your chances of getting into med-school, or in the case of the OP, into one of the top medical schools (Harvard, Duke, Penn).
Now, I know what you're thinking. I just stated a tautology - the best premed program for you is which one will help you the most. Actually, it really isn't a tautology, for the following reasons.
The fact is, med-school admissions is not only extremely competitive (in that about half of all premeds around the country who apply to med-school get rejected from every single one they apply to), but also extremely grade-driven. Simply put, if you don't have high grades, then you won't be seriously considered. Your application will be thrown away before it ever gets read by a human being.
The upshot of this is that you should go to a premed program where you believe you will be able to get the top grades that med-schools demand. This is generally boils down to a combination of a school that has lots of grade inflation (for example, many of the Ivies, Stanford, etc.) and/or a school where you know you are clearly better than the average student, such that you will be able to dominate the classes.
This is why I take the admittedly controversial stand and say that many of the premed programs that people think are strong really aren't very good at all. For example, the premed programs at Johns Hopkins, MIT, Berkeley, and, yes, WUSL really aren't that good when you truly think about it. And I say that for one reason. The reality is that all of these schools are well known for harsh and rough grading, and that sort of thing absolutely kills you when it comes to med-school admission. Will a lot of premeds from these programs get into med-school? Sure, because those schools are top schools and have top-notch student bodies, and so their chances of getting into med-school were high to begin with. My point is that these programs do not really boost their students chances of getting into med-school, and in many cases actually hurt them, because of the harsh, competitive grading. What's the point of going to a supposedly 'elite' premed-program and then getting grades that are so low that you wind up not getting in anywhere? You probably would have been better off going to a 'non-elite' premed program and gotten high grades there.
Case in point, consider MIT. I think we would all agree that MIT is an extremely prominent school that is well known for tough grading and lots and lots of work. For those MIT premeds who apply to med-school, only about 75% of them actually get in to at least on med-school, which means that 25% get rejected from every single med-school they applied to. That's right, every single one. And these statistics doesn't even count those MIT students who want to go to med-school but know that their grades aren't good enough, so they don't even bother to apply. Furthermore, the GPA of the average MIT student who was admitted to med-school was a 3.7/4, and I think we all agree that pulling those kinds of grades is extremely difficult at a place like MIT.
Contrast that with the premeds at Princeton. I think nobody will seriously dispute that the average quality of students at Princeton is roughly about the same as that at MIT. I also think we would agree that MIT is probably a harder school than Princeton, in terms of grading and workload. So you would think that med-schools admissions committees would know this too and compensate accordingly (by demanding higher grades from Princeton premeds relative to MIT premeds, and by simply admitting a lower percentage of Princeton premeds than MIT premeds). Yet the data shows that about 90% of all Princeton premeds get admitted to med-school, compared to 75% at MIT. Furthermore, the average GPA of admitted Princeton premeds is about 3.4/4 to 3.5/4, which is significantly lower than the 3.7/4 average GPA of admitted MIT premeds.
To summarize, MIT and Princeton's student bodies are probably roughly equivalent academically, and MIT is a harder school that gives out significantly lower grades, and yet Princeton premeds get into med-school at a higher rate and with lower grades than do MIT premeds. Use Occam's Razor and I think you will draw the conclusion that MIT premeds are not only not helped by the harder workload and tougher grading at MIT, they may actually be getting hurt by it. And the bottom line conclusion is that MIT is not as good of a place to do premed than is Princeton, because MIT is less successful in getting its students into med-school - and for premed programs, ultimately that's all that really matters. If you're not boosting the chances of your students to get into med-school, then at the end of the day, you're not really a good premed program, despite what the rankings might say. The whole point of a premed program is, after all, to help students get into medical school.
I understand this is a controversial stance, which is why I've tried to back it with data. I don't have the statistics for the premed programs at WU or JHU on me, but I don't think it would substantially different from the MIT data, because I know that WU and JHU (especially JHU) are schools that have little if any grade inflation. In any case, I highly doubt that any of these schools have premed programs that are as successful in getting students into med-school than Princeton does (and by extension, also probably Harvard, Yale, and Stanford, for HYPS have about the same grade inflation).
The point is, if you are absolutely sure you want to be a doctor, then you want to go to a premed program that maximizes your chances of getting into med-school. The fact is, one of the hardest part about becoming a doctor, arguably the hardest part, is simply getting admitted into med-school in the first place. If you can't get in, then your medical career is over before it ever really started. What's the point of going to a 'prestige' pre-med program like JHU or WU or MIT and then discovering that you can't get into med-school? I can assure you that that 25% of MIT premeds who got rejected everywhere are seriously rethinking whether they should have gone to MIT at all, and more specifically, whether they'd be in med-school right now had they gone someplace else for premed.