Although that professor might really want to work with you, s/he should understand if you decide to attended another school with a better program. I selected the school I'm at now because the professors I'm working with are some of the best in the country for my field. Before I selected this school, however, I was considering getting my M.A. where I got my undergrad. Before I left, I had a meeting with the incoming faculty of my alma mater. He plainly stated his position; he wanted me to stay there and help him and another incoming professor rebuild the program (they lost some key faculty members the previous two years). He said that he and the other professor were relatively new to the field, but the professors where I am at currently are well-established and will be able to open more doors for me. He's been right so far. I have had several opportunities that I've taken that would not have been available to me had I stayed at my alma mater.
I have a tremendous amount of respect for him. He knew that I had a better chance at my current school and would not (did not) fault me for choosing it, but he wasn't afraid to express his wishes for me staying there.
You are lucky to work with such understanding people. My problem is that the professors at the private school think their program is better than the public one and technically it is. It has a top ranking in my field while the public school is not as high. At the same time, I would say the professors at both schools are both of the same rank and recognition, with the one at the public one being a bit more well-known and a huge name in the subfield. The professor at the private school also works in my subfield but also dabbles in many other subfields as well.
The professors at the private school were nice enough to tell me they thought I was really suitable for their program and they look forward to having me there, but their tone is very insistent. They have actually sent a number of notes congratulating me as if I had already accepted. I've not given commitments to any university, especially this one. So I am worried that they won't take my polite decline of their offer with understanding, especially since I most probably will end up at the public university next door and will also be taking classes with them and I assume will be interacting with them on a fairly regular basis. I've heard mixed feedback about the private school and also heard that several students have left in the past due to problems in the department. Another issue is that the main professor in the private school that works on my topic will be retiring soon, which would leave me without anyone in my subfield. On the other hand, the public school, has at least two professors who are top scholars in the field and I understand they will stay put at the university.
I would like to say that I'm grateful to have the choice of choosing where to do my PhD, I know not everyone gets this chance. But I never thought that accepting or declining an offer would need diplomatic maneuvers.
Thanks
