This is the most important design decision in your gold farm. It decides what aggression methods are available for your farm and the shape that it can have.
Almost every aspect of your gold farm relies on the kill method you use. If you use fall damage to kill the pigmen the storage system doesn't usually have to be that complex and it also can't use player aggression to lure the pigmen. Looting is by far the better method. It does have some drawbacks however. The storage system has to be much more complex due to the large ammount of golden swords and more gold that it produces. This is a mojor issue for inexperienced gold farm designers because they don't know how to design a good storage system. Even with this limitation it does produce 350% more gold than fall damage. If you afked a fall damage farm you would usually have to afk above the farm which limits the height of it. However the height limitation on this type of farm is that if you are too close to the nether roof you will have to do alot of spawn proofing underneath it.