Hey guys, in my experience and opinion, i'd have to say i would choose to use Apexi Power filters and a heat sheild/partition. Remember guys the more noise its making doesnt necessarily mean its better, it most likely means more resistance/harder for your engine to breathe. Things such as what turbo your car has obviously play a big role as to how much noise will be heard from the filter. A plain bearing (bush type) turbo will spool up slightly slower therefore making a more laboured induction noise. Apexi make aluminium and also carbon fibre induction boxes that look pretty kool but are hell expensive too. There are templates available online where you can cut out aluminium and make your own custom induction box. I guess the advantage of having it fully enclosed would be that the cops can't do you for it. Im sure i heard that if its enclosed its ok to have...
Anyways this is just my opinion :-)