I would definitely go to Oracle Database 19c. Patching ends for 18c in June 2021, whereas it ends for 19c in March 2023 (with paid option to extend to 2026). Since, 19c is the long-term support release there are many more customer (and will be many more customers) on this release.
On the other hand, Oracle Database 18c has proven to be a very stable release, so if you don't mind upgrading again next year, then you could go to 18c. However, I would expect most customers going to Oracle Database 19c.
19c is also known as 188.8.131.52 and 18c is 184.108.40.206., but these aren't simply minor patches. Oracle Multlimedia, for example, has been deprecated in 18c and is no longer available in 19c. You better check the new features and release documentation and check what applies to your installation or configuration.