Which API Should I Use in Salesforce? and What are the different API's available in salesforce.com?

Which API Should I Use in Salesforce? and
What are the different API's available in salesforce.com?

following user permission need:
User Permissions Needed – API Enabled under the profile level

Application Programming Interface (API)

API Name	What It’s For	When to Use It	Protocol	Data Format	Communication
REST API	Accessing objects in your organization using REST.	You want to leverage the REST architecture to integrate with your organization. No WSDL requirement.Well-suited for browser-based applications, mobile apps, and highly-interactive social applications.	REST	JSON, XML	Synchronous
SOAP API	Integrating your organization’s data with other applications using SOAP.	You have pre-existing middleware services that need to work with WSDLs and XML data.	SOAP/WSDL	XML	Synchronous
Chatter REST API	Accessing Chatter feeds and social data such as users, groups, followers, and files using REST.	You want to integrateChatter into a variety of applications, such as mobile apps, intranet sites, and third-party Web applications.	REST	JSON,   XML	Synchronous (photos are processed asynchronously)
Bulk API	Loading or deleting large numbers of records.	You have over a million records to process and speed is a requirement.	REST	csv,xml	Asynchronous
Metadata API	Managing customizations in your organization and building tools that can manage the metadata model, not the data itself.	You want to migrate changes, such as custom object definitions and page layouts, from a sandbox to your production environment.	SOAP/WSDL	XML	Asynchronous
Streaming API	Providing a stream of data reflecting data changes in your organization.	You need near real-time notifications of when records are created or updated.	Bayeux	JSON	Asynchronous (stream of data)
Apex REST API	Building your own REST API in Apex. ExposesApex classes as RESTful Web services.	You need to build custom JSON responses or you want to expose custom functionality that you implemented in Apex.	REST	JSON, XML, Custom	Synchronous
Apex SOAP API	Creating custom SOAP Web services in Apex. Exposes Apex classes as SOAP Web services.	You need to build custom XML responses or you want to expose custom functionality that you implemented in Apex .	SOAP/WSDL	XML	Synchronous
Tooling API	Building custom development tools forForce.com applications	You want to add functionality to your existing development and integration tools or you want to build specialized development tools for a specific application or service.	REST and SOAP	JSON, XML, Custom	Asynchronous

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