[libc]

They are both great platforms. The Pi can in theory do everything an Arduino can while also allowing access to a full Linux based OS (or RISC, but I can't comment on that). If you were limited to just one, I'd say to get the Pi just because you can do more with it. The Pi is also better if you're more interested in the software side of things.

In my opinion the Arduino is a bit more mature overall and has better tutorials for beginners starting out in electronics. You can also use it with Windows or OSX if Linux isn't your thing. Even if your long term goal is to do electronics on the Raspberry Pi, I'd recommend getting an Arduino to learn on because it is simpler and doesn't require Linux knowledge.