[ubuntu] [B]Which V.Box configuration is better?[/B]

I need to install ubuntu and windows7 on my machine and work simultaneously.

I have a modest CPU speed, but with 8 GB of memory..

Would it be better to use ubuntu as my primary OS, and install Windows7 on virtual box?

Or would if be better to do it the other way around.. Windows7 as primary and Ubuntu on VBox?