Do you still care how to choose min SDK version? Last two years Google guys spent lot of efforts in order to make Android more fluent for vendors. The most popular devices now regularly receive firmware updates automatically. From the developer's point of view it's a fantastic! We don't need to care about dino-phones anymore.
You can see it by yourself from
latest statistics from Google. Devices with API 19 and higher now cover more than 70% of market! This means we can use lot of modern features of Android KitKat, Lollipop and Marshmallow without tons of libraries and crutches.
You can find
more details here.