What's my best option for Windows 8?

So at the moment my desktop is running Windows 7, but using the license key on the back of the actual machine. This is because the recovery partition is corrupt and I had to re install Windows by using a version I burned onto a disc myself (form a torrent) and so had to use the product key on the back, not the 'OEM system key (?)'.

Which version of Windows 8 should I get? The upgrade version, or the system builder version, given that my recovery partition in corrupt and the product key for Windows 7 may no longer work after?