http://pcpartpicker.com/parts/os/
Windows 8 is superior, and the interface issue is easily avoided with Start8. Seriously, the interface is basically IDENTICAL.
There are a LOT of differences under the hood so I strongly recommend getting W8.
*Also, Windows 8 OEM is transferrable, but Windows 7 OEM is not. Looking up that info correctly is a huge pain but that is how it works. I really can't think of one good reason to recommend Windows 7.