I tried to look for ranking lists, but could not find a reliable one.
NYU. Also, in another thread someone noted the University of Pittsburgh.
Check out the Philosophical Gourmet Report on undergraduate programs.
http://34.239.13.205/index.php/undergraduate-study/
You will be unlikely to find an authoritative ranking of undergraduate philosophy departments. For this major, you may want to begin by researching colleges at which professor-led, discussion-based classes would be typical. Look into Vassar, Wesleyan, Swarthmore, Haverford, Hamilton, Pomona . . .
I agree with @merc81—a ranking that tells you which department has better-published professors is not worth your time. Philosophy is the ultimate read-and-discuss major, and you want the best opportunity to be in smaller classes taught by professors. Obviously the better LACs should be on your list, but many larger schools may have small classes as well.
fwiw here is the most recent ranking published. http://dailynous.com/2018/03/01/2018-qs-philosophy-rankings/
Within the field, Philosophical Gourmet is generally considered a reliable graduate ranking, which will show rankings in subfields etc. But that is meaningful only for someone who is dead set on getting Ph.D, in Philosophy after undergrad. Philosophy Ph.Ds – like many fields – have a very very very difficult getting a full time, tenure track job in. Philosophy graduate students choose a specific school to work with specific professors, so the overall college ranking is not meaningful, just that department and the availability of that professor to work closely with you. Current top ranked graduate programs in a range of subfields include NYU, Pittsburgh, Columbia, Riverside etc.
For an undergrad who wants a robust department as a major but is not focused on a career as an academic – look at department websites of schools of interest to see if they have faculty teaching in core areas – Ethics, Metaphysics, Ancient, Modern, 20th century, Logic etc. See how often courses across these subfields are offered, and how many faculty are working in them. Philosophy is usually a small major at most schools so after the Intro classes, class size is usually pretty small.
I’d look for colleges that offer a lot of classes & have a lot of professors in a wide variety of topics. Breadth is important at the undergrad level. U of Toronto has a huge & excellent philosophy department, and at Canadian universities students usually take a higher % of their classes in their major than is typical at American colleges.