I've got some of each. The pin-locks tend to be shorter and fatter so you may not be able to fit as many in a space the same "floor plan" as ball locks.
I actually prefer pin locks because it's impossible to mix up the fittings in a dark freezer, but I think the use of them is not as popular as ball locks so I sometimes have to provide my own fittings at club events. In other words, pin locks seem to be in the minority around here.