Really, no reason at all to trek to Chungking Mansions to change money! There are plenty of exchange places in every shopping district.
Worldwide House if you need pesos, but not otherwise.
WWH is not just for pesos. But it takes some checking between different places here and then a bit of bargaining (i.e. not going by the boards).
Berlin is best, barring the queues. But it really depends on the sum being exchanged.