There's no real advantage from one to the other.
As to why most people around here have ball locks is a bit of a geographic thing in my opinion. There are many folks in the Halifax area that have pin locks because there used to be a Coca Cola plant (or distributor) there and its a bit easier to source pin locks.
Around here, there have been Pepsi plants and distributors. That's why alot of folks have pepsi kegs.
Same in the US; folks in the south mainly have pin locks because Coke is in Atlanta. Folks in the midwest have ball locks.
This is simply one theory.