Surely you would want still air around the carb inlets if possibe but not at to restrict the airflow, hence the HRC airbox. Some bikes (particular unfaired ones) would suffer more at speeds with no airbox at all - although the generally dont go as quick anyway .

A through flow of air around the carbs would make it very unpredictable as to how much air it will be able to suck in.

My vote is HRC airbox if you want to MOD it.....otherwise leave it standard.