Xbox 360 4gb or 250gb?

I want to offer my wife an Xbox 360+Kinect for Christmas, and I wonder if should get the 4GB version or the 250GB version.
More details:
 - the console will be used mostly for casual gaming (Danse central, fitness)

- I am a former PC gamer (last game seriously played was Bioshock.... since I got a day job!), so I might get tempted to get Deus Ex, Elder Scroll... but unfortunately nothing intensive due to the day job I still got.