I'd suggest Duke since it is a more prestigious program unless you have made your plans for your future goal in Cali. Cali is good, but the cost of living is not worth it if you don't have a thorough plan for your future.
As far as I know, Purdue has some very good professors working in statistical learning. And ISU is more concentrated on the theory of statistics, e.g. probability, measure theory and real analysis.
I would suggest OSU as well. First off, it has a better environment, as your friend said. You will spend at least four years doing Ph.D. You don't want to end up in a small town like Cornell, ISU, TAMU... Actually, TAMU is not as bad as the other two. And the ranking of OSU is good.
But to make sure, what is your research area or where your interests lie in?