Why use MySQL?
It's free.
Widely used, so there is plenty of support, examples,
tutorials.
Better at performing some tasks such as jumping to records
without first cycling through the previous records.
It runs on Windows, Windows Server and *nix machines
It is continually being improved (ongoing development)
It can use transactions (ie rollback several update/inserts, if
something fails)
Supports live backups, table locking, basically anything any
other database can do.