I've used both. Never had an issue with either. They both do the job they say they do. With magic jack I just plug it into an existing usb port and either use an attached phone or a pc headset to talk with. Can call anywhere in the US or Canada free of charge or any magic jack phone number anywhere in the world.

Same idea with skype except I don't need any hardware, just install the program sign in and go. Certainly not an expert as I generally use it strictly for text related stuff, but have used the voip features here and there.

Voice quality on both is generally good, but like anything else internet related depends a lot on network conditions (and the computer it is attached to)

Personally for phone use I prefer magic jack. I like the fact that it's a separate piece of hardware that I can take with me anywhere and for $40.00 it's hard to beat that price. From what I've read you can use magic jack internationally as long as you have a phone to plug it into. But I've never tried it so can't say if that's true or not.