There are valid arguments for both positive and negative pressure, I'm not sure one has been proven 'better' than the other, especially as each case is different.
With our case we are fortunate in that the cabling provides almost no obstruction, which is a good start. Since hot air rises, it makes most sense to use the top-most and rear fans for exhaust. To balance that, in CFM terms, we can use the front fans for intake. Depending on your exact set-up, you will likely have postive/negative CFM. But I don't think it matters much.
If you had a lot more exhaust than intake (say, 4 fans vs 2) then you may find you do indeed get a significant amount of dust in. Filters help sometimes, but in other cases the filter creates resistance, and the air (which naturally find the place of least resistance) just enters elsewhere! Some people find that a set-up like this cools better, though, due to hot air being expelled faster and because there are less dead-spots.
If, on the other hand, you had 4 intakes vs 2 exhausts, you have the opposite problem. Dust won't be an issue as the pressure will likely prevent much from entering, but the actual temperature of the air may be warmer and you are more likely to develop dead spots that are not expelled. That said, those spots are usually a result of poor circulation, and with our case that's not something that you could readily achieve!
My own preference is to try to keep a balance between both, and if there has to be a compromise I lean on the side of positive pressure, mainly because I don't like dust. I think, with all fans running full speed, I am something like +10 at the moment.
Is that the AI Suite you're referring to for controlling the fans? I remember reading about Fan Xpert but was warned by many that the AI Suite is really tough to remove and so didn't bother with it. Might have been an error on my part, there!
