DWF said..
Square nose paddles straighter.
Yes, DWF, and therefore has more drive to early take-off.
The pro is the drive with parallel outline brings to the nose and the con is the pearling and catching of the nose's corners on the way down the face from cut back or reentry.
Mattlew, the pro of the square nose is the amount of buoyancy you can hide in the nose angles. If you want to do it very short, go square nose. That way to save foam in the nose angles allows you to go thinner board.