Upgrading from mysql 5.7 on FreeBSD to mariadb or MySQL8
Any version declared "GA" is "good".

5.7 is only one major version behind what Oracle is providing.  There have been a lot of improvements in 8.0, but, as with any upgrade, you may or may not be affected.

MariaDB 10.3 is a good parallel to 5.7, but there could be differences -- in features and in Optimizations.

It is good that you are eager to upgrade, but since you had troubles with 8.0, I think it is reasonable to stay with 5.7 for a while.  (Some people are struggling with upgrading from 5.5 or even older versions!)