Well, neither IE9 nor MSN are part of the OS, you don't have to use either one with anything.
The "best" depends on what you want to use it for, you don't just ask for a "best car" do you? Post what you will do with the laptop. Your only real options are Win 7 or some type of Linux. I guess you can toss XP/Vista in there but that also depends on if your laptop model has drivers for those, and neither of them are as good as Win 7 unless you have software compatibility issues.