If you are not so sure about what version of Windows 7 is the right one for you here is a page that will help you in this task. 

Now, with nearly fully-functional versions of each product edition available to the public, I thought I’d provide a series of tables comparing each Windows 7 product editon… …It’s early yet, and things will no doubt change, so I’ll be updating these tables as needed going forward. But even at this early stage, I believe these tables will help you pick which Windows 7 product edition makes the most sense for you, based on your needs and wants.

Paul Thurrott has done a very good job summarizing all the options available in each version.