My choice would be Apache JMeter, It's free and opensource plus it comes with lots of plugins and extendability. Apache JMeter needs a small amount of a learning curve and a basic understanding of Network, Protocols (TCP/IP ports, HTTP(S) and REST/SOAP, etc.) for initial setup. But it doesn't require programming skills. it has a nice record and playback option. You can still carry on without the developer skillset if you follow these steps. 1. Take backup. 2. Start recording and interact with the application. 3. stop recording and save the test case. This will give you your test-bed, after this, after these steps, every time just do Restore from backup and then Playback and observer results.

If you have longer recordings then an understanding of how to modify the recorded scripts will come handy.

For some of the advanced features such as Configuring variables, implementing loops, throttling adding think time, and automating test scaling to the number of users will require good planning of test scenarios and a Developer experience but this is true for any tool (even loader.io)

Disclaimer: I work at k6, and I recommend you try our tool.

It might require some coding skills, but we support a few options to record a user session to autogenerate the load test. Read How to record a browser session with k6 OSS.

The k6 Cloud also supports recording a user session with a Browser Extension. Additionally, it provides a Test Builder UI to generate a load test for testing APIs.

If you have questions or need help, you can ask on Slack and the Community forum.

I use Postman because of the ease of team-management, using workspaces and teams, runner, collections, environment variables, test-scripts (post execution), variable management (pre and post execution), folders (inside collections, for better management of APIs), newman, easy-ci-integration (and probably a few more things that I am not able to recall right now).

I recommend Postman because it's easy to use with history option. Also, it has very great features like runner, collections, test scripts runners, defining environment variables and simple exporting and importing data.

I use Swagger UI because it's an easy tool for end-consumers to visualize and test our APIs. It focuses on that ! And it's directly embedded and delivered with the APIs. Postman's built-in tools aren't bad, but their main focus isn't the documentation and also, they are hosted outside the project.