Hi Joanna,
I've used both Starry Night Pro and The Sky.
Personally, I prefer the appearance of Starry Night Pro but The Sky is the more recognised package amongst professionals. Starry Night Por is a little more eye-candish than The Sky but the Sky may have a few more features, depending on which version you get.
If you don't need telescope control and just want a piece of software to accurately simulate the night sky, I would strongly suggest you try Stellarium first. It's free and by far the most eye-pleasing of all the astronomical programs I've ever used. This is what I have used in the past for any of my talks that require displaying an image of the night sky on an overhead projector.
Also note Cartes du Ceil is a program can also simulate the night sky and can control the telescope. This program is also free.
I would recommend that you try both Stellarium and Cartes du Ceil before parting with your cash for another program.
Hope this helps,
  