When I built mine I had a copy of 7 retail so I could have used it, BUT I want to continue using the old system so I opted to get 8.1 and didn't really like the setup at first and ended up getting a program called StartIsBack for $3 I think and it is great, once your used to some of the features you start to really like it and it seems to boot a little faster than 7 does also but that was not a big point to me (I can wait 15 seconds longer on a boot and not care. I do like 8.1 with the StartIsBack added.
I have Start8 myself. My fiance refused to install it though - she said she would just deal with it lol. She seems to be used to it now, I think.