You need GLA to level 22 for Provoke regardless of what tank you play, and you'll want it to 34 if you're going to take tanking seriously. I also like PLD as a beginners tank because it forces you to learn how to recognize aggro and understand how it works if you want to do your job affectively. On the other hand the learning curve of aggro management on GLA has been known to scare people off of tanking, so that depends on your type of person.

Otherwise WAR is fun (particularly in the later levels), and you learn to focus DPS rather than party support.