MySQL or Oracle Associate Certification?
Forgive me for sounding a little biased, but I would recommend MySQL DBA Certification for you without hesitation. I say this without reservation because that is how I become a MySQL DBA.

I actually wrote an earlier post about making such a transition from school, from a willing developer, from an unwilling developer, and from a sysadmin.

I also wrote another post on how DBAs should properly interact with developers and project managers.

I would personally say MySQL positions are very underrated in the eyes of most companies, yet the demand is out there. I feel have been respected because of my certification (unique experience, result vary based on who hires). I certified back in August 2007 with my employer paying for the course. At that time, no instructor-led MySQL course was required for certification. Now that Oracle owns MySQL, that may have changed. Please check with Oracle on that.

Most companies that hire MySQL DBAs may expect you to know everything else, (Linux, Apache, Nagios, Munin, JBoss, PHP, Perl, Python, etc). Many other companies may use only MySQL. Overall, you have to be selective when looking. The more disciplines/skills you have outside of MySQL, the better your employment chances are.

What makes the most money is a different story. Hands down, Oracle DBA/Developers make more money. Certification is more expensive because Oracle Associate requires only an exam. To earn deeper Certifications in Oracle, you take necessary exam(s) and you must attend at least one instructor-led Oracle course (Exams run about $200-$300, while the courses run $3,000/each). While Oracle Certification is more rigorous, the respect you get for working with Oracle and the money will indeed come. You can pretty much write your own ticket an an OCP. Going for OCA is a good start.

Regardless of MySQL, Oracle or any other RDBMS, nothing can substitute for having working experience. Due diligence in all DBAs takes will train you to certify quickly.

If there are any Oracle gurus out there, please post your own answers on Oracle as I am sure there a lot more positive things that can be said for Oracle.