As with other tools, the outcome dictates the tool choice. A chasing hammer with a slightly domed face is perfect for flattening out wire shapes like coils or earwires. A 1 or 2lb brass mallet is the tool of choice for striking daps or disc cutters. A rawhide mallet is used to shape metal without marking.
A good hammer can't do the job without having the proper surface to strike on. Jewelry Tools carries a variety of bench blocks and anvils to help make your strike true every time.