Both 19c (19.25.0.0) and 23ai (23.6.0.24.10) drivers are supported with Oracle Database 19c. 23ai JDBC driver is the most recent release, hence it has more features than 19c and to answer your question:

1. As you are already using JDK11, hence it is better to use ojdbc11.jar which is compiled with JDK11. ojdbc8.jar is meant for those who are still using JDK8 and because of that they cannot use the ojdbc11.jar.
2. No performance implications of JDBC 4.3 over JDBC 4.2.