Which API Should I Use?

You can use multiple APIs to interact with Marketing Cloud. Each API is designed to handle different needs and use cases. However, as a Marketing Cloud developer, you’re most likely to interact with the platform and Data Cloud APIs.

Use the Salesforce platform APIs to create standard Salesforce objects, such as contacts and campaigns.

REST API: Most REST API requests are handled synchronously, but a few are asynchronous. Use REST API to query, create, and modify data in your Salesforce org using JSON requests. You can also use this API to send transactional messages and manage Salesforce users. An advantage of using REST API is that most modern applications and programming languages include features that make it easier to implement REST calls. REST API also supports composite requests, with which you can send multiple requests in a single call.
SOAP API: Like REST API, most SOAP API requests are synchronous, but a few are asynchronous. SOAP API performs many of the same functions as REST API. An advantage of using SOAP API is that it supports Web Services Security (WS-Security) headers, which can provide end-to-end security for API requests. SOAP requests are typically larger and more complex than their REST equivalents. As a result, they require more bandwidth, memory, and processing power.
Bulk API 2.0: Bulk API 2.0 is an asynchronous, REST-based API for the Salesforce platform. You can use it to create, manage, and query large volumes of data in your Salesforce org. Any request that includes 2,000 records or more is a good candidate for Bulk API 2.0. Because it’s asynchronous, requests to Bulk API 2.0 require you to issue separate requests to create a job, upload content, check the status of the job, and close the job when it’s complete.
Metadata API: Use Metadata API to read and manage flows in Marketing Cloud. For example, Metadata API is helpful when you want to move flows from a development environment to your production environment.

Connect API is a REST-based API. Use Connect API to upload and publish content such as images and emails to your Marketing Cloud content workspace.

Data Cloud API is a REST-based API that contains both streaming (synchronous) and bulk (asynchronous) components. Use the streaming operations to create, update, or delete individual records synchronously. For example, you can use the streaming operations to add transaction data to Data Cloud from an external commerce platform as new records are generated. The bulk operations are helpful for bringing large quantities of data into Data Cloud asynchronously. For example, you can use bulk requests to synchronize Data Cloud with an external database.