FWIW this is the ranking from
www.phds.org based purely on quality of teaching
1. Massachusetts Inst of Technology
2. Princeton University
3. University of Chicago
4. Stanford University
5. Harvard University
6. University of Minnesota
7. University of California-Berkeley
8. Northwestern University
9. Yale University
10. University of Rochester
11. University of Pennsylvania
12. Univ of California-San Diego
13. California Institute Technology
14. University of Wisconsin-Madison
15. University of Michigan
16. Univ of California-Los Angeles
17. Columbia University
18. Brown University
19. Cornell University
20. Duke University