Amsterdam is great. Commercial sex in other parts of NL is often touted as being even better...cheaper, much better attitude among sex workers, less clock watching, etc.
The smart money, however, says the FKK clubs in Germany are the way to go.
Legal or not there is a lot of commercial sex in and near formerly communist eastern european countries. However, there is also a great deal of organized crime involved with a level of violence not often seen in the west. Horror stories of sex workers kidnapped and forced into the business are not uncommon.
Dark horse...I read somewhere that Tallinn Estonia has a remarkable commercial sex scene at bargain prices. However, the above comments about organized crime apply.