SCT xcal2 is the way to go, IMO. It costs a little more, but is worth the money.
Obviously, the chip is just that...a chip you put into your car with the tune on it.
The Xcal2 gives you a lot more than just a tune. First and foremost, you can reflash your ECU with updated tunes and return it to stock if you need to take it to the dealer. You can also read DTC's (and clear them), adjust air/fuel ratio's, spark timing, and readjust your guages for different sized wheels. The xcal also comes with the software to do data logging....you plug the xcal in to your car, then a usb cable from the xcal to a laptop. Fire up the software and you can log a very wide variety of things going on in your ride.
If you have the money, I would suggest getting the xcal....you just get more.