I want full internet access and preferably USB printing too so I know I need to use the Vbox from Oracle directly and not the Ubuntu repos.

But what difference in performance would I see between the two? I've used Virtualbox a lot so I know how to set it up well, but KVM I've only tried a few times. Can the screen resolution go beyond 1024x768 or whatever it is?

What benefit is there to having KVM be part of the kernel? KVM seems like it's a lot more difficult to set up. The host will be 12.04.