If its a new hard drive in an old computer use whatever you already were using.
If its a new computer your cheapest option will probably be OEM. With OEM you will be limited to using windows only on that computer though. If you want the freedom to move windows to a different computer later (after removing it from the current computer) then get a Retail copy.
The Retail copys are also sometimes called Full like on newegg's website: http://www.newegg.com/Product/Produ...116716&cm_re=windows_7-_-32-116-716-_-Product
If its a new computer your cheapest option will probably be OEM. With OEM you will be limited to using windows only on that computer though. If you want the freedom to move windows to a different computer later (after removing it from the current computer) then get a Retail copy.
The Retail copys are also sometimes called Full like on newegg's website: http://www.newegg.com/Product/Produ...116716&cm_re=windows_7-_-32-116-716-_-Product
