The Raspberry Pi is a full on computer. It’s crazy that such a small device has that much power behind it. It doesn’t have all of the built-in sensors that the other two devices have so it features in less missions.
The Raspberry Pi website has loads of projects for you to try out and a whole community of people waiting to help. I’d recommend joining either the online forums or searching for a local Raspberry Jam, Code Club or CoderDojo. There’s nothing like meeting fellow coders face-to-face and plotting to save the world together