Hell, I even had a use case where serial GC was actually the correct choice (small job runner process that needed to be extremely low memory overhead). It's nice having options, and most of those options are extremely good for the use cases they were designed for.

Ok, which one do I choose then, with what configuration? How much time do I need to spend on this research?

How do I verify that they are actually better? Is the overall performance of my program better? Because that's what I care about. I of course do include memory usage in "performance".

Do you need extra-low latency, even at very high percentile and are willing to give away a bit of throughput for it? ZGC

At almost every other case: G1 (the default, just don't add any flags).

Do you want to trade off using less memory at the price of some throughput? Decrease heap size, otherwise don't add anything.

That's it, in most cases just use the default.