Pull up when you can - pull down if you must.
As mentioned before with TTL you needed very low values of pull down resistors (about 300R) and that gave poor noise immunity and high currents. Where as a pull up could be 4k7.
With some drive circuits like that on the ones on the arduino chip it is irrelevant.
However the absolute chip limit of 200mA is the current limit of the supply pin. By mixing them you could have 200mA of current source and 200mA of current sink and still stay within the limits. 
Actually keep that limit to less than 150mA anyway.