Which is the cheapest and best option Windows OEM VS. Retail

[BigCave]

Hey all!,
I am building a computer for a client and realized I can buy a Windows key off of Kinguin for very cheap. I know people who have bought keys from Kinguin, all of them have had great success. My client states he wont upgrade from windows 8.1 to 10. Does this mean buying the OEM version of Windows 8 is the better option, compared to a retail key. Will they be identical operating system wise?
Thanks!

 

[drtweak]

Doesn't really matter these days. They don't even really have OEM and Retail anymore. OEM is more so the Retail now and System builder is for people who build machines and then sell them.

Just get what ever is cheaper as long as it is legit