
As a level 30 rdm, I have to kind of take offense to the description that after certain levels we loose our importance. I just recently leveled up my non-advanced jobs to at least 14(except white mage--lvl 11). Upto this point the only job where you can do both attack things(black mage spells) and healing(white mage spells) without needing another mage or job is rdm. I realize down the road white and black mage's get far more powerful verisons of these spells,but you still need another mage to heal(in the case of black mages), or a meele job(in the case of white mages), whereas the rdm can do both. Well I realize this game is based on partying, you still have to look at each job indivudally when comparing 2.
To answer the question of the original post:I guess it depends on what is needed in a party at the time, what the party is trying to do, and most importantly which job you are the most comfortable doing at the time.
Remember, the best way to figure out the better job between 2 of them is to actually try them out for a few levels(at least). Once you have tried them out it should become apperant to you whic one is better for you.