First off, congratulations on getting two great offers!
It sounds to me like you felt OSU was the right choice from the beginning, but now you're having second thoughts because of a perceived prestige difference. While I do think that it's really important to work with a well-known mentor, for what it's worth, I also think that feeling comfortable where you'll be spending the next 5ish years of your life is important. Moreover, it would concern me a bit to commit to a program without having communicated with my potential mentor. I don't think his/her unresponsiveness bodes well. After all, working with a star in your field really only pays off if that person is interested in your academic development and is willing to go to bat for you when it comes to funding and, eventually, finding a job.
Just my two cents...good luck with your decision!