Depends on your fans. You can get fans that pull in more than the exhaust and still have positive pressure with 2 and 2. I have 2 intake and three exhaust due to two 280mm radiators and all my stuff stays nice and cool. Dust isn’t that big of an issue if you spray canned air occasionally.
That whole positive/negative pressure thing isn't very important... unless your case is vacuum-sealed.
Dust is going to accumulate regardless, just clean the case out a few times a year. I do it once a month-every other month... perhaps a bit overkill.
That said, 2:2 fan setup would be a better balance over 1:3.
+1^ on the dust problem. Positive vs negative pressure is kind of moot with computer cases. They have multiple entrance and exit points. Bottom line: keep as much air flow through the case as possible w/o creating a noisy tornado. 2 x in and 2 x out sounds fine. Remember, top and back for exhaust and front, bottom, and side for intake. (under most normal conditions)