Round ports produce a wider variety of frequencies than say a square or rectangle. You also have to take into account that if you go with a slot or square port depending on tuning it will have a turn in it. Turns in a port hurt flow and cause turbulance this limits spl. I personally would go with aeroports, less length/room required for the same tune, less turbulance and port noise plus ease of tuning... JMHO, Polo.
