From my understanding of it I would have thought it depends on your chassis height and therefore positioning of front suspension.
If your design relies on a high chassis then maybe a hoover nose maximises the air flow to the back of the car by having some going between the pylons and the rest over the side of the nose and under the front suspension.
If the chassis is lower then a Mclaren type nose will make more use of the space between the nose pylons for air flow as the suspension components are in a lower position and airflow over the top is not as useful to them.
Whichever one is better, the chassis cannot be as high next year (regulation changes) so Mercedes and Ferrari will have to change their design philosophy for the front suspension after this year. Many seem to have gone for a lower chassis (Mclaren the lowest so far), this may help in the long-run, maybe the merc and ferrari will have a slight advantage for this year? who knows? bring on testing!
I hope I made sense