I prefer using Katalon Studio. Before learning API testing, I has learned Katalon to do Automation testing. It has a friendly UI and is very easy to use. It fully supports Web, Android, iOS and API testing on all operating system. So I also use this tool to learn API tesing.
I completed exercise 1 using Katalon.
But I think the most powerful feature of this tool is Custom Keyword. This feature help users create their own keywords to solve their business logic issues which no any automation tool can handle.
That why I choose Katalon Studio for Automation testing as well as API testing 
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