Hi there! I actually found myself in the same dilemma this cycle, albeit for Epi, so please feel free to take my words cum grano salis. For me, it came down to potential research/networking opportunities (the costs of attendance were pretty much equated for me, because I was fortunate to receive a merit award from Columbia, so my advice will not include financial considerations--but that does not make those considerations any less important!). Both are wonderful places with much to offer, so I found myself drawing up lists of pros and cons: Yale's small class size greatly appealed to me because there seemed to be a stronger chance of developing more solid relationships with faculty and with my peers. On the other hand, the deliberately small size of the school worried me a little because it seems that it might limit possible research opportunities. Columbia is a much larger and apparently impersonal school, which is daunting, but it is very well-recognized in this field, has an intensive curriculum, and provides a broader range of research, in my opinion.
I think it ultimately comes down to what you are looking for in your program and the environment that you feel best suits you. I recommend talking to as many people from either institution as you possibly can and objectively assessing the information they give you. I spoke to both a professor and student from Yale who gave me a good picture of the school, I felt. Then, I visited Columbia and sat in on a class, not so much for content as much as to observe the class dynamic; an Epidemiology professor also reached out to me and was able to speak to me by phone about public health and research at Columbia. I personally felt that the class was very respectful towards the lecturers, asked thoughtful questions, and made meaningful contributions to their discussion. Class dynamic is especially important to me (I've been in too many science classes where students seem to try to one-up each other, vying for the professor's attention in increasingly irksome manners, and I'd love to see more collaborative than competitive environments as I go forward in my education
). I also really appreciated the professor's willingness to talk to me (not so impersonal as I'd initially assumed), and, more minor consideration, I love New York City while I'm young and still have the energy for it, so all that decided me--I ended up committing to Columbia Epi.
This isn't a cunning advertisement for Columbia, though, I promise! I truly mean it when I say that you should speak to as many people as possible before April 15th. I know that sounds like a very generic answer, but it's the best I have to offer, and it is what worked for me while making this decision. Ask yourself: what school will provide me the opportunities I want for my professional future? Along whom would I like to learn? With which professors might I like to study (actually, if there is a particular person whom you might be interested in knowing/working with/learning from at a given school don't discount that)? And truly ask yourself what environment is most conducive to your learning and see which place better fits that.
This might have been a longer answer than you expected, and it may not have all the information you wanted, but I hope that it is useful in some capacity, or at least that you find another soon-to-be MPH candidate's perspective somewhat helpful.
But honestly, whatever your decision, it can't be a bad one; you have two fantastic options. Congratulations on your acceptances and good luck!