I took Yale over Harvard for Environmental Health, but it was for money, not for a sense of superior education.
That said, I am perfectly confident in the education and research experience I've received here. I spent most of the summer at Berkeley with a brief stint at a CDC conference, and was very happy to have had my Yale education-- I was able to keep right up with, and sometimes lead, the epi conversations being had by PhDs, PH professionals, and leading researchers in the field. I attribute this directly to the strong foundation in Epi, Stats and critical thinking** that I have so far received at Yale. I cannot speak directly to Chronic Epi, but I think the Epi profs here are as good as any I've encountered, and the small size allows for a good deal of one-on-one and, if you find a prof doing the right research, a better chance of getting a research gig... though because I've never actually studied at another public health school, I can't really be all that objective in my comparisons.
As Veggie Monster suggested, there's been a good deal written on this-- more specifically on Yale's low US News rank (13th, I think?), high NRC rank (3rd-ish), and perceived reputation.
Best of luck!
werD
** Honestly, I think we could be pushed to "critically think" a little more than we are, but you can still get a good deal of it if you're motivated to do so.