Depends on what you want to use it for. If you are a normal home user, I recommend Home Premium or perhaps Professional. Starter and Home Basic are too basic, and Ultimate has many features you probably won't need.
Agreed with that.HP and Professional are very good versions,I wouldn't get the starter,very basic, wouldnt even let you change the wallpaper. Home basic,lack of features. I got ultimate, it runs good but if you're looking at price-wise then go for the ones Herr_Koos said.