I don't like the octopus, sorry. Not only is GitHub the immediate association with octopus, but I don't like the actual image. Sorry.
Also, I think @dom96 and @Araq should just pick the mascot without an open discussion. It's the kind of decision that doesn't require opinions from the public, much like naming the language. It's a matter of taste, which means there's no solution to satisfy everyone by definition.
I think that every rationalization about why to pick a mascot will not be understood. It has to be something that just looks nice.
Unfortunately, I don't like very much any of the previous proposals. If a mascot is needed (is it?), make sure it is drawn by a professional designer