My experience goes as far as installing it and not doing much with it.
I do however know that MariaDB was created by the original guys that created MySQL, it's designed to be a drop-in replacement for MySQL (if you're using MySQL 5.5, MariaDB 5.5 should be exactly the same, not sure how the 10 range matches up)
From what I've seen, MariaDB beats MySQL in every benchmark, so at least it has the same or better performance than MySQL.