The DS18B20 differs from the DS18S20 in an important respect: the designer can select the desired resolution by using the configuration register. This flexibility allows the user to reduce the ADC conversion time and conserve power if higher resolutions are not required. Some modifications to code may be necessary when replacing the DS1821 but both DS18B20 and DS18S20 are available in TO-92. 
We have an application note describing the differences between the DS18b20 and DS18S20 at the link below. 

Comparison of the DS18B20 and DS18S20 1-Wire® Digital Thermometers: