brand new imac.. switching mac

Bootcamp is faster, but requires you to reboot the computer each time you want to switch environments.

VMs gives a slight performance penalty, due to having two OSes running at the same time, and to the limited amount of RAM used by Windows, but you get the bonus of being able to run Windows apps seamlessly side to side with OS X apps (fusion mode).

Maybe this can help: http://guides.macrumors.com/Booting_Windows_on_the_Mac

In shot, BC allows the full resources of the Mac to be used with Windows, though a restart is required, while running Windows via a VM will allow you to use Mac OS X with Windows side by side, though Windows will not be as fast as with BC and it might slow down your Mac OS X experience too.

Running Windows in a VM can be done with not so CPU and GPU intensive applications, while BC will allow you to fully utilise your Mac's hardware components.

Btw, a more descriptive thread title could get you a more experienced audience.

I would not recommend running Windows on a Mac. It give you this horrid Windows startup screen every time you boot into Windows.