Both options are good. Java 8 has the advantage of being able to run executable jars. This is good for all kinds of utilities.
With OpenJDK 11 it is easier to build distributable packages and it is the way to go forward.
Last question please -
If I will rewrite my project from b4J4.0 to actual B4J version with OPENJDK11
and
after this I will recognize that OPENJDK11 is not good for me and I will use JAVA8 - must I do some changes in the code in the future? (between openjdk11 and java8?)
and please: https://openjdk.java.net/legal/gplv2+ce.html it does it mean that with OPENJDK11 I can distribute my projects 100% free and for my users it will be 100% free, it is true? I want to create only free app and I want have free distribution and easy instalation.
EDIT: For users - I have migrate my big project from b4j4.0 to b4j7.32 with openjdk11 without troubles, it is absolute easy and intuitive. Big thanks to Anywhere Team.