Here is my take on the most common open source tools:

- Gatling: https://gatling.io/ - Great tool. Fast, full-featured, flexible, well documented. Main drawback is that you script it in Scala... UX for automation purposes could be better also.

- Tsung: http://tsung.erlang-projects.org/ - Also great. Very fast, scalable, many features. Main drawback is the XML-based DSL (Domain Specific Language) that is somewhat of a pain to use.

- Vegeta: https://github.com/tsenart/vegeta - Good for simple testing of API end points with a fixed RPS rate. No scripting capability.

- Apachebench: https://httpd.apache.org/docs/2.4/programs/ab.html - Single-threaded but very, very fast so will outperform many tools that can use multiple CPU cores. Best tool around if all you want to do is hit one single, static URL and get results printed on screen. Lacks scripting.

- Jmeter: http://jmeter.apache.org/ - Very fast, tons of features, but painful UX (especially for an automation workflow). Biggest community with the most plugins/extensions/whatnot.

- Siege: https://www.joedog.org/siege-home/ - Moderately fast but doesn't scale. Buggy and will crash regularly. Large measurement error. Inconsistent UI. Only reason to use is that it is an alternative to Apachebench if you want to hit a list of URLs, rather than just a single URL.

- Artillery: https://artillery.io/ - Great UX for automation. However, it lacks scripting capabilities, is slow and single-threaded and introduces a large measurement error.

- Locust: https://locust.io/ - Great scripting capabilities (in pure Python), with a very nice API. However, it is the slowest tool I have seen and introduces the most measurement error of any tool also.

- Wrk: https://github.com/wg/wrk - Fastest tool in the universe. About 25x faster than Locust. 3x faster than Jmeter. Scriptable in Lua. Drawbacks are limited output options/reporting and a scripting API that is callback-based, so painful to use for scripting user scenario flows.

- The Grinder: http://grinder.sourceforge.net/ - Fast, scriptable in Jython (Python dialect) with a nice API. Main drawback is that it is an almost dead open source project - very few updates in recent years.

- k6: https://k6.io/ (bias warning: I am involved in the k6 project) - The B3ST tool!! ;) Anyway... it is fast, scriptable in Javascript (ES6), has a very nice UX and scripting API and works for both functional and performance testing (and is excellent for automation). Good docs too (https://docs.k6.io).

General advice:

- If you're a Java-centric shop, take a look at Jmeter or Gatling, or perhaps Siege (all are Java apps) and you'll feel at home. You should probably start with Gatling, because it is more modern than Jmeter, with better UX, and Siege is kind of on its way out.

- If you want to automate your load tests, want to test an API, and prefer to write test cases in code rather than some limited DSL, then I think k6 is the tool you should look at. Only reason not to, is if you don't want to use Javascript.

- If you want to run complex, manual load tests of a web site (e.g. record user interactions and then simulate the same behaviour in a load test) you should look at Gatling or Jmeter primarily. Perhaps Tsung.