It's good to be overweight! According to this study studying a group for the ten years 2003 to 2013, the BMI associated with the lowest all-cause mortality is 27.0. My current BMI is ... 27.2. Yay!
On the other hand, I should note that so far as I can tell there is vastly more noise than signal in studies of this nature. This particular study looked at nearly 100,000 Danes in that period. It wouldn't surprise me a bit if 100,000 Americans, Japanese, or Egyptians were studied, they'd get completely different results. Probably even a different set of 100,000 Danes would get a different result!
But I like this one :)