IMO it's personal preference. A windscreen is supposed to block airflow or maybe more appropriately, it's supposed to direct airflow around your head and body. Some folks can't stand wind hitting their head. Some folks can't stand the noise of air flowing around their helmet. Some folks are exactly the opposite. So, the windscreeen itself is entirely a matter of personal taste. The trick to a windscreen is getting the airflow layer positioned either over the top of your helmet or underneath the chin. If the aiflow layer hits your helmet anywhere in between, you get helmet buffeting. You can easily feel where this layer is while you ride just by using your hand. You will feel where it flows in relation to your head.
Three factors play into helmet buffeting. First is the height of your head in relation to the height of your windscreen. Second is the design of the windscreen (height, width, angle). Third is the helmet design. Some helmets are more prone to buffeting than others.
All three of these factors have a combined effect. You may go through 3 helmets, 4 windscreens, and 2 brackets before you find a combo that works for you. If you look, you will see quite a few threads on this board regarding which windscreen/bracket works best for someone of a given body size. So basically, you need to figure out what it is you like.
My personal preference is no screen.
Last edited by jcstratt; 08-28-2010 at 05:38 PM.