My guess would be that Jefferson and maybe TR were the most intelligent presidents. Obama strikes me as someone who has just been given everything he has accomplished. He is not stupid but seems just slightly above average to me.
Very possibly the least intelligent president.
I once saw an article somewhere that had John Quincy Adams rated as the most intelligent. I'm just throwing it out there, and cannot defend it. (It also had John F. Kennedy among the least intelligent, with a tested I.Q. of 119.)