It depends on what is your hardware configuration because we need to match the hardware and software of the computer, otherwise it will be frustrating but generally speaking for general computer configuration Windows XP and Windows 7 very good.
Any versions of Windows 7 are good to me because they have all the features that we want to meet with.
this will highly depend on your requirements. If it fits your need then that will be the best for you. On the other hand Ultimate has more features and cost
I'm a big fan of windows but the least version, Windows 7, is truly the most perfect operation system in existence. I'm really looking forward on Win8