each platform have something unique to offer, depend on your personal objective. I plan on building a personal robot assistant and so far I will need raspberry pie, arduino and ez-b. Do some research first , see what work for you. I have the ez-b and it is mind blowing.

The arduino has been mentioned a lot in the past. I doubt there will be direct support for using it with ARC without an EZ-B however DJ has mentioned something about arduino support or control or something with a future update. I can't remember exactly what since it doesn't interest me in the slightest but search and you may find it (I suspect in a topic about the revolution)

Arduino is just hardware you can load firmware onto. Ezb controller has roots in arduino as far as hardware. The board is shaped and arranged to accept arduino shields and sensors. This is very important because of the abundance of pre existing shields and sensors at a low price. Besides hardware compatibility that is where similarities end. The controller connects to a PC and takes advantage of a PC power and expanded memory to function faster than existing micro controllers as well as additional features like processed video for motion , facial recognition ,color tracking etc. Really for any single controller you just can't beat it.