So neither is an upstream of each other at this point, they're a fork. And contrary to what people are saying in this thread, as of 10.0 MariaDB is no longer a drop-in replacement for the most recent version of Oracle MySQL and MariaDB's developers are no longer committing to porting all Oracle MySQL features. So MariaDB is no longer a Percona Server-like "MySQL plus goodies" upgrade proposition (and it really hasn't been for a long time - the 5.x series is still at 5.5). MariaDB actually will tell you which MySQL 5.6 features they support:
You're better off on Oracle MySQL. There's other tradeoffs, depending on what you use. What bugs the heck out of me is how a fair number of MariaDB advocates spread FUD about Oracle (if you judge them by their track record, they've committed to improving and maintaining MySQL -- they're not perfect, but that's no excuse to harp about stuff they COULD do when there's no evidence they WANT to sabotage MySQL to force you to switch to Oracle), and want to turn the debate into a holy war rather than focusing on letting everyone pick the best tool for the task.
I think you should research MariaDB some more -- there are a lot of reasons to use it, and a lot of companies are switching. In fact, just today we upgraded our Zimbra cluster and was surprised to see they had made the switch from MySQL to MariaDB. This isn't "fud" as you put it... but rather a better product for a lot of reasons.
> You're better off on Oracle MySQL.
Hardly true, given the two db's are mostly the same except that the creator is now making newer and better changes in the 10.x branch of MariaDB (Monty left Oracle just like most Sun employees due to inner-politics and fighting that is regular at Oracle).
https://mariadb.com/blog/mysql-56-vs-mariadb-100
So if you need, for instance, MySQL 5.6's partitioning improvements:
https://blogs.oracle.com/MySQL/entry/mysql_5_6_is_a
You're better off on Oracle MySQL. There's other tradeoffs, depending on what you use. What bugs the heck out of me is how a fair number of MariaDB advocates spread FUD about Oracle (if you judge them by their track record, they've committed to improving and maintaining MySQL -- they're not perfect, but that's no excuse to harp about stuff they COULD do when there's no evidence they WANT to sabotage MySQL to force you to switch to Oracle), and want to turn the debate into a holy war rather than focusing on letting everyone pick the best tool for the task.