I hear different top rankings from different people, usually (from what I can tell--in my opinion) depending on their current geographical location. I was under the impression that NYU was number one and/but very closely followed by Brown. Stanford is on par with Brown and then Northwestern following that. Then CUNY.
All that said, one program I hear great things about from scholars is the Theatre Historiography Ph.D at Minnesota. It seems to me to be a real up-and-coming program that is well-respected by those in the field and only gaining more and more recognition as it establishes itself. SUNY-Buffalo is another new program that is quickly garnering recognition.
Performance Studies and Theatre Studies programs--respectively--are difficult to rank. I think this is because, unlike other humanities and especially the sciences, they are newer (well, in the case of Performance Studies) and are still establishing themselves as legitimate fields. Seriously, theater programs are often the first to go in the cuts universities are making in financial straits. I've read at least two articles in journals that are essentially "in defense of theater studies" manifestos. It's bad out there. As a result, it's difficult for administrators or whoever it is that decides on rankings to determine what programs should be recognized. Performance Studies and Theater Studies are also very interdisciplinary in their very origins, so that's another hitch in ranking programs.
So uh...hope that helps? Hah.