One of the biggest advantages Skype, which by the way has an app for the iPad, has over FaceTime app is that you can make audio and video calls to other Skype users around the world on more types of hardware. This includes calling Windows and Mac computers, Android devices, Windows Phone handsets and even certain Skype-enabled televisions and Blu-ray players. Skype-to-Skype calls are free, and for a bit of money, you can call regular telephone numbers.
On the other hand, FaceTime app is also free for one-to-one video calls, but it only works on certain Apple-made products. These include camera-equipped iOS devices made within the past few years and Macs running OS X 10.6 and later. Still, because it is integrated into the operating system, FaceTime can be a little easier to set up and use if you plan to chat only with people carrying Apple gear.
Which one do you prefer?