What are you trying to accomplish? Windows 7 is a minor upgrade so most hardware should continue to work. I have heard good things but you must realize that the beta expires in early 2010 and you will probably have to re-install then.
It always depends on your preferences of Windows Operating System. Those versions of software are developed for certain users. If you feel that you are already satisfied with the features of Windows Vista OS, then there is no reason to experiment and try other Operating System like Windows 7, just stick with what you have.