8.1 or 8
which will update to 8.1 anyway
8 has better license that lets you move it to another computer at some future time . Its easy to customize it to behave like 7 with either a paid start button program like Start 8 , or with the free Classic Shell which works perfectly on my comp .
If you are building a media center then 7 can be the better option . MC is not included with 8 Home