There are a few more factors that are involved in positive and negative air pressures. Where your components are placed, how much heat they put out, where your case fans are located, the size of them, and how many Cubic Feet per Minute of air the fans push (also known as CFM)
Positive air pressure is having more intake than exhaust, and having filters on your intakes will help reduce dust.
Negative air pressure is more exhaust than intake, and are harder to keep dust free.
It's a matter of preference as far as positive or negative pressure goes.
Personally, I own an antec 1200 v3 case. which you can see here: http://www.newegg.com/Product/Product.aspx?Item=N82E16811129100
Although on the lower exhaust, I have it switched as an intake with my corsair cwch60 liquid cooler, with the stock antec fan, and the fan that comes with the cooler. This allows for better CPU cooling, and doesn't mess up airflow, too much.
Here is a link with a little more in depth information than what I have to offer.http://www.silverstonetek.com/techtalk_cont.php?tid=wh_positive&area=usa