Ideal way to start 'Database Server' in PostgreSQL 11
I would prefer option A. 

Using systemctl ensures the service is properly (re)started when the computer is (re)started.

As far as the location of the data directory is concerned: the manual shows some defaults. The actual location of the data directory is essentially driven by the packager that built the RPM (or whatever package the OS uses) and the standards the distribution expects or uses. You could also put it under /databasedata/postgres/pg11/data if you want, or /very/important/data/postgres