A few weeks back, the Raspberry Pi foundation officially announced a brand new release of Raspbian which is the go-to operating system for the Raspberry Pi. While there are certainly many Linux (none of which are Android) based options out there which will work with the Raspberry Pi, Raspbian is developed in house by the foundation and you can be assured that someone has your back when you stumble upon a problem.
Being a beginner slash amateur in the Raspberry Pi world, I still rely heavily on Raspbian to guide me to controlling electronics through the GPIO pins from the various tutorials made available on the internet. Sure, I have played around with Windows 10 IoT Core and the OpenELEC system but Raspbian gives me that assurance about the product that I have invested some money onto. It is not just a desktop operating system but it is a learning platform for me.