Why choosing one Operating System ... if you've got plenty of harddisk space for partitioning ...

I always run more than one Windows ... 3 different ones on different partitions - in case there is a problem, i can always start another Windows and can rework the faulty Windows version or partitions from there.

I've got WinXP SP2 twice installed on two different partitions - and one Vista Ultimate on a third partition - installed last in the row, to get the Vista bootmanager to combine all three Windows versions and to choose easy, what i want to start and work with.

This way i can always fall back to the best working system for a certain application or whatever and like mentioned above, i've always got a working system running (sure, only as long your boot partition isn't damaged  ;) , but that can be fixed, too, with a little more work again, as long as nothing else is damaged...).