Yeah its personal preference really.
I prefer negative....I tried positive once and my temps went up 2 degrees. Also I vacuum my room 2 times a week and I have hardly ANY dust...I air every month still and I do a fan cleaning with Isopropyl alcohol every 6 months to get the dust that wont blow off the fins of the fan.
Personal preference once again.
Also I find the pantyhose idea HORRIBLE even super stretched it stops 50% of the fan flow and kills your fans within 6 months and increases heat.....just get a 30 dollar Air tank and go to the gas station and fill it up...will clean 10 PCs which a can of air is $5 and it will do 4-5.