Which Salesforce API Do I Use in Integration ?

Choosing the right API for your integration needs is an important decision. 
Here’s some information on most commonly used APIs, including supported protocols, data formats, communication paradigms, and use cases. 

Treat this blog as a reference you can return to when you’re considering which API to use.

API Name	Protocol	Data Format	Communication
REST API	REST	JSON, XML	Synchronous
SOAP API	SOAP (WSDL)	XML	Synchronous
Chatter REST API	REST	JSON, XML	Synchronous (photos are processed asynchronously)
User Interface API	REST	JSON	Synchronous
Analytics REST API	REST	JSON, XML	Synchronous
Bulk API	REST	CSV, JSON, XML	Asynchronous
Metadata API	SOAP (WSDL)	XML	Asynchronous
Streaming API	Bayeux	JSON	Asynchronous (stream of data)
Apex REST API	REST	JSON, XML, Custom	Synchronous
Apex SOAP API	SOAP (WSDL)	XML	Synchronous
Tooling API	REST or SOAP (WSDL)	JSON, XML, Custom	Synchronous

Read More: When To Use Salesforce REST API  
                   When To Use Salesforce SOAP API 
                   When To Use Salesforce Bulk API 
                   When To Use Salesforce Chatter API