The main difference between the two has to be their software applications. The Microsoft Office Standard Program only comes with Outlook, Powerpoint, Excel, and Word. For Microsoft Office Professional, there are a lot of programs that are available such as Access, Publisher, Business Contact Manager, and all of the other programs that are available in the Standard version.
It is more ideal that you will get the official release if you only need something that can be used at home. This is also more ideal if you only need basic programs. If in case you would need something for your business, then the professional version will come in handy.