For a PhD, the quality of the school or the program isn't nearly as important as the quality of the person who will be your research advisor. In fact, I would say that your research advisor is all-important in choosing a graduate program.
If you have contacts in the fields that you would like to work in, find out where they got their PhDs and what they thought of their advisors and any other advisors in the school. Talk to your PhD colleagues in your current position about their graduate programs. Do some literature searches and find the key people doing seminal research in the areas that interest you. Look up the publication records and group sizes of the schools you are thinking about applying to and figure out who you would want to work for. Go to some ACS meetings and talk to the people presenting about their research groups, both students and professors.
Some things about a research advisor that will make your life easier during and after grad school:
- moderate sized research group - large enough to have plenty of people to ask for help, small enough that you can make an impact.
- length of time to get a PhD - there are people out there that like to have lots of grad students, especially later stage grad students that know how to do research, and somehow manage to make it take 6 or 7 years to get the PhD.
- money - if the PhD is good at getting grants and funding, it will make it much easier for you to do research. Sad but true. Reusing silica gel and disposable pipettes and trying to get data out of antique equipment that nobody remembers how to maintain will really slow down your progress.
- contacts - your main purpose in getting a PhD is getting a better job. It helps if your research advisor is also a major consultant in the industry you intend to work in.
- reputation - face it, there are a lot of places where being able to say "I worked for Dr. xxx" will mean more than anything you ever learned. Especially when Dr. xxx is the acknowledged authority in the field you are working in.
Picking your research advisor will fix the course of your grad school and immediate post-grad life. Choose carefully. I have deliberately picked some of the more cynical bases for choice and left out many of the personal choices that will help you stay happy (or at least sane) in your graduate program, but they are in fact extremely important and few people thinking about entering grad school even realize they might be important. I have no doubt that you will be able to extend this list dramatically when you sit down and think about it!
Best of luck