If you will be a tank on a raid, you'll want to be a Guardian for the sheer fact they get the best defense. You will do nothing but stand there and take a beating keeping agro as everyone else burns the mob down.
Bad part is that of all fighters, your DPS is among the lowest. Fights will drag on into infinity, as you slowly chip away at the mob, and the Priest will back you up with his low-medium nukes.
It will be a long slow road, but you'll eventually get there.