Since I am at the moment computer less, I don't "use" any, but iI was using java 9...
BUT, since java 11 opens again the possibility to use GUI apps on raspberry pi, once I get a new laptop (hopefully soon) I will use java11
I mean "learn" in the extended way: from installing, to configuring, check if every piece of my code would still be supported and would still work as before.
I don't think it's going to be exactly like replacing with a new build of the same version. It's going to be a full QE project for me.
And I'm not disputing about the advantages to migrate, which I understand and plan to.
Now I'm curious to know why you're asking us this question. Are you planning to drop Java 8 support anytime soon?