Although I have no problems using Windows 8.1, I was rather surprised to see the 64-bit OEM version sold out at newegg.com while there's still plenty of Windows 7 OEM in stock.
Well, it's cheaper to buy 8.1 now then 7, so for someone with a new build it makes sense to buy 8. (unless it's business)
8.1 is back in stock now. The OEM version is $99.99, same as Win 7 Home Premium OEM. If I was assembling an all-new PC with no OS, I'd go with 8.1. But, I still have an unused Win 7 3-pack at home.
Sell that 3-Pack on eBay or Amazon... I'm sure lots of people need it.