Real estate is the most proven asset class in the history of the world. That is true, but is it the best in this current environment? Maybe. If your time horizon is longer than 7 years, then I would say yes to real estate. If you are looking at 7 years or less, I would say that it's not the best investment out there.
Also, Real estate is such a broad category that at any point in time, one section of real estate will be performing great while others will not. We can all see the issues with Office space right now, but during the 90's to 2000's it was an amazing asset. Residential has been a winner for a while now, but what's to say that demographics cause issues in 15 years, much like with China? So can real estate be the best investment out there, yes some of it can be, but then for others it will be the worse.
The best investment for anyone is something they can easily understand and to sleep at night not worrying about it. For some that is real estate, others its bonds, others its stocks. For me, its real estate.