Which Windows version?

Hello,

I have been recently thinking of using Bootcamp so I can access programs such as Fruity Loops and other music VSTs and programs, as well as games that only work for Windows. I have looked into buying Windows 7 to do this, but I am not quite sure which version is best to buy. I've found many different types on Amazon including Ultimate and such, but some of these have different prices and different specifications. Which one is best for what I want to do? A link to it would be appreciated!

Thanks.